Prenatal Screening Tests
“Prenatal screening tests” is a blanket term that covers a variety of testing your doctor may recommend or you may choose to have during pregnancy.
Some prenatal screening tests are done to determine whether a baby is likely to have specific health conditions or chromosomal abnormalities, like Down syndrome.
Chances are, your doctor mentioned these screening tests at your very first prenatal appointment, because most are done during the first and second trimesters.
This type of screening test can only provide your risk, or probability, that a particular condition exists. It doesn’t guarantee that something will happen. They’re usually noninvasive and optional, though recommended by most OBs.
When the results are positive, further diagnostic tests — some that may be more invasive — can provide more definitive answers for you and your doctor.
Other prenatal screening tests are routine procedures that look for health issues that may affect you, your pregnancy, or your baby. One example is the glucose tolerance test, which checks for gestational diabetes — which, by the way, is manageable.
Pregnant people who have a higher risk of having a child with certain conditions are usually offered additional screening tests. For example, if you’ve lived in regions where tuberculosis is common, your doctor may order a tuberculin (TB) skin test.
When are prenatal screening tests done?
First trimester screening tests can begin as early as 10 weeks. These usually involve blood tests and an ultrasound. They test your baby’s overall development and check to see if your baby is at risk for genetic conditions, such as Down syndrome.
They also check your baby for heart abnormalities, cystic fibrosis, and other developmental concerns.
This is all pretty heavy. But what’s much more exciting to many people is that these super early screening tests can also determine your baby’s sex. Specifically, the blood draw that can tell you if you’re having a boy or girl is the non-invasive prenatal test (NIPT). The NIPT blood draw isn’t available at all doctor’s offices, and your healthcare provider may not offer it, depending on your age and other risk factors. But if you’re interested in this option, be sure to ask
Second trimester screening tests may occur between 14 and 18 weeks. They can involve a blood test, which tests whether you’re at risk for having a child with Down syndrome or neural tube defects.
Ultrasounds, which allow technicians or doctors to look carefully at baby’s anatomy, typically take place around between 18 and 22 weeks.
If any of these screening tests show abnormal results, you may have follow-up screens or diagnostic tests that give your doctor more detailed information about your baby.
First trimester screening test
Ultrasound
An ultrasound uses sound waves to create an image of the baby in the uterus.
The test is used to determine the size and position of your baby, confirm how far along you are, and find any potential abnormalities in the structure of your baby’s growing bones and organs.
A special ultrasound, called a nuchal translucency ultrasound, is performed between the 11th and 14th weeks of pregnancy. This ultrasound checks the accumulation of fluid at the back of your baby’s neck.
When there’s more fluid than normal, this means there’s a higher risk of Down syndrome. (But it’s not conclusive.)
Early blood tests
During the first trimester, your doctor can order two types of blood tests called a sequential integrated screening test and a serum integrated screening.
They’re used to measure the levels of certain substances in your blood, namely, pregnancy-associated plasma protein-A and a hormone called human chorionic gonadotropin.(Double Marker test)
Abnormal levels of either mean there’s a higher risk of a chromosome abnormality.
At your first prenatal visit, your blood may also be tested to see if you’re immunized against rubella and to screen for syphilis, hepatitis B, and HIV. Your blood will also likely be checked for anemia.
A blood test will also be used to check your blood type and Rh factor, which determines your Rh compatibility with your growing baby. You can be either Rh-positive or Rh-negative.
Most people are Rh-positive, but if you’re Rh-negative, your body will produce antibodies that will affect any subsequent pregnancies.
When there’s an Rh incompatibility, most women will be given a shot of Rh-immune globulin at 28 weeks and again a few days after delivery.
Incompatibility occurs if a woman is Rh-negative and her baby is Rh-positive. If the woman is Rh-negative and her baby’s positive, she’ll need the shot. If her baby is Rh-negative, she won’t.
Note: There’s not a noninvasive way to determine your baby’s blood type until after they’re born.
Chorionic villus sampling
Chorionic villus sampling (CVS) is an invasive screening test that involves taking a small piece of tissue from the placenta. Your doctor may suggest this test following abnormal results from an earlier noninvasive screen.
It’s usually performed between the 10th and 12th weeks and is used to test for chromosomal abnormalities, like Down syndrome, and genetic conditions, such as cystic fibrosis.
There are two types of CVS. One type tests through the belly, which is called a transabdominal test, and one type tests through the cervix, which is called a transcervical test.
Testing has some side effects, like cramps or spotting. There’s also a small risk of miscarriage. This is an optional test — you don’t have to get it done if you don’t want to.
Second trimester screening tests
Ultrasound
During the second trimester, a more detailed ultrasound, which is often called a fetal anatomy survey, is used to evaluate the baby carefully from head to toe for any developmental issues.
While a second-trimester ultrasound can’t rule out all potential issues with your baby — that’s what the additional screens described below can assist with — it’s helpful for your OB to eyeball baby’s body parts, and fun for you to see those fingers and toes, too!
Blood tests
A triple or a quadruple marker test is done during the second trimester of pregnancy, ideally during the 15th to 20th week. A quadruple marker is more sensitive than a triple marker test and a mother is usually asked to go for the same to ascertain genetic defects in the foetus.
Name of the test | Suitable Timing | Parameter Tested | Accuracy Level |
Double Marker | 10-13th week | Free Beta HCG & PAPP-A | 75-80% |
Triple Marker | 15-20th week | AFP,HCG & Estriol | 60-70% |
Quadruple Test | 15-20th week | AFP, HCG & Estriol & Inhibin A | 75-80% |
A quad marker screening is typically offered if you start prenatal care too late to receive either the serum integrated screening or the sequential integrated screening.
It has a lower detection rate for Down syndrome and other issues than a sequential integrated screening test or serum integrated screening test.
Glucose screening
A glucose screening test checks for gestational diabetes, a condition that can develop during pregnancy. It’s usually temporary and resolves after delivery.
This glucose screening test is pretty standard for everyone, whether you’re considered high risk or not. And, note: You can develop gestational diabetes even if you’ve not had diabetes before your pregnancy.
Gestational diabetes can increase your potential need for a caesarean delivery because babies of mothers with gestational diabetes are usually born larger. Your baby may also have low blood sugar in the days following delivery.
Some doctors’ offices start with a shorter glucose screening, where you’ll drink a syrupy solution, have your blood drawn about an hour later, and then have your blood sugar levels checked.
If your levels are high, your doc will schedule a longer glucose tolerance test, where you’ll fast before the procedure, have your blood drawn for a fasting blood sugar level, drink a sugary solution, then have your blood levels checked once an hour for three hours.
Some doctors prefer to solely perform the longer glucose tolerance test. And this longer one may be performed if you have certain risk factors for gestational diabetes.
If you do test positive for gestational diabetes, you have a higher risk of developing diabetes within the following 10 years, so you should get the test again after the pregnancy.
Amniocentesis
During amniocentesis, you’ll have amniotic fluid removed from your uterus for testing. Amniotic fluid surrounds the baby during pregnancy. It contains fetal cells with the same genetic makeup as the baby, as well as various chemicals produced by the baby’s body.
An amniocentesis tests for genetic abnormalities, such as Down syndrome and spina bifida. A genetic amniocentesis is usually performed after week 15 of the pregnancy. It may be considered if:
- a prenatal screening test showed abnormal results
- you had a chromosomal abnormality during a previous pregnancy
- you’re 35 or older
- you have a family history of a specific genetic disorder
- you or your partner is a known carrier of a genetic disorder
Third trimester screening test
Group B Strep screening
Group B Streptococcus (GBS) is a type of bacteria that can cause serious infections in pregnant women and newborns. GBS is often found in the following areas in healthy women:
- mouth
- throat
- lower intestinal tract
- Vagina
GBS in the vagina generally isn’t harmful to you, regardless of whether you’re pregnant. However, it can be very harmful to a newborn baby who is born vaginally and doesn’t yet have a robust immune system. GBS can cause serious infections in babies exposed during birth.
You can be screened for GBS with a swab taken from your vagina and rectum at 36 to 37 weeks. If you test positive for GBS, you’ll receive antibiotics while you’re in labor to reduce your baby’s risk of contracting a GBS infection.
The double marker test, also known as maternal serum screening, is part of a more comprehensive screening called the first trimester screening. It’s not a definitive test. Instead, it’s classified as a predictive test, which means its results report the likelihood of chromosomal abnormalities.
Specifically, this test screens for blood levels of both free beta-human chorionic gonadotrophin (beta-hCG) and pregnancy-associated plasma protein A (PAPP-A).
In a typical pregnancy, there will be either 22 pairs of XX chromosomes in female fetuses or 22 pairs of XY chromosomes in male fetuses.
A trisomy is a chromosomal condition in which there are extra chromosomes, such as the following:
- Down syndrome. This common trisomy is also referred to as trisomy 21 because there’s an extra copy of chromosome 21.
- Trisomy 18 and trisomy 13. These common chromosomal abnormalities involve an extra copy of chromosome 18 (Edward’s syndrome) or chromosome 13 (Patau’s syndrome).
Levels of hCG and PAPP-A may be either higher or lower than “normal” in pregnancies with these chromosomal abnormalities.
However, blood levels alone don’t produce your results. Instead, the blood test is used along with an ultrasound called a nuchal translucency (NT) scan, which examines the clear tissue at the back of your baby’s neck.
Why a double marker test is done
The first trimester screening — double marker test and NT scan — isn’t mandatory. That said, the screening (and others like the cell-free DNA test) is recommended if you’re over the age of 35 or may have an elevated risk of chromosomal issues, such as if you have a family history of certain conditions.
It’s important to remember that the result only tells you whether there’s an increased risk of trisomies. It doesn’t definitively determine whether your baby has any abnormalities.
Before deciding whether you want a double marker test, you might ask yourself what the results would mean to you in the long run.
· Would knowing about possible abnormalities ease or worsen your anxiety?
· Would you want to go for more invasive testing if you receive a result that indicates heightened risk?
· Would the results change how you’d manage your pregnancy?
It’s all about personal choice and your own health history, so there’s really no right or wrong answers to your questions.
Timing of the double marker test
There’s a relatively slim time window during which the double marker test can be performed. Your healthcare provider will have you make an appointment for sometime near the end of your first trimester or possibly very early in the second trimester.
More specifically, you’ll have your blood drawn sometime between weeks 11 and 14.
Standard results for the double marker test
You’ll receive a low-, moderate-, or high-risk result.
Low-risk (“screen-negative”) is considered a “normal” result and means that there’s a low probability of your baby having chromosomal abnormalities.
If your result is in the normal range, you’ll only be recommended for further testing if there’s some other indicator (like family history, age, etc.) or if you desire to learn more for some other reason.
Still, a low-risk result doesn’t always mean your baby won’t have an issue. And it’s important to note that the first trimester screening only looks at markers for Down syndrome, trisomy 13, and trisomy 18 — not other conditions.
Abnormal results for the double marker test
If your screening comes back as moderate- or high-risk (“screen-positive”) for abnormalities, you may choose to go over your result with a genetic counselor to learn more.
Your result can be confirmed with more definitive and sometimes more invasive tests, such as noninvasive prenatal testing (NIPT), amniocentesis, or chorionic villous sampling. While some of these tests carry some risk to your pregnancy, they provide a definitive result.
Since the double marker test is done early on in your pregnancy, the information gives you time to make important decisions about further testing, medical treatments, and the overall management of your pregnancy and delivery.
Knowing your risk may also help you prepare for the potential you’ll have a child with special needs and allow you to find the support you’ll need.
Double marker test vs. NT scan
For the most accurate results, the double marker test (blood test) and NT scan (ultrasound) are used together in the first trimester screening. The information gathered from both tests is what gives the result of a low-, moderate-, or high-risk of abnormalities.
When performed without the double marker test, the NT scan is less effective at detecting potential abnormalities.
The NT scan allows your healthcare provider to use sound waves to collect a real-time image of your baby. It’s performed around the same time as your double marker test.
At that point in pregnancy — late in the first trimester — your healthcare provider can measure the size of the clear area on the back of your baby’s neck. Your doctor will also assess the development of the nasal bone, which may be another indicator of a trisomy.
These measurements are combined with your blood results and age-related risk. They’re all calculated together to produce your baby’s potential risk of Down syndrome, trisomy 13, or trisomy 18.
What You'll Find Out from an NT Scan During Pregnancy
Pregnancy screenings take place during the first, second, and third trimesters. The first trimester screening is a type of prenatal testing that provides your doctor with early information about your baby’s health — namely your baby’s risk for chromosome abnormalities.
A nuchal translucency (NT) scan screens your baby for these abnormalities. This test is typically scheduled between weeks 11 and 13 of pregnancy.
What’s the purpose of an NT scan?
An NT scan is a common screening test that occurs during the first trimester of pregnancy. This test measures the size of the clear tissue, called the nuchal translucency, at the back of your baby’s neck.
It’s not unusual for a fetus to have fluid or clear space at the back of their neck. But too much clear space can indicate Down syndrome, or might show another chromosome abnormality like Patau syndrome or Edwards syndrome.
Our body cells have many parts, including a nucleus. The nucleus holds our genetic material. In most cases, the nucleus has 23 pairs of chromosomes, which are equally inherited from both parents.
Individuals born with Down syndrome have an extra copy of chromosome 21. Down syndrome, which can’t be cured, causes developmental delays and distinct physical characteristics.
These include:
- a small stature
- eyes with an upward slant
- low muscle tone
This condition affects 1 in every 700 babies born in the United States. It’s one of the most common genetic conditions.
Patau syndrome and Edwards syndrome are rare and often fatal chromosome abnormalities. Unfortunately, most babies born with these abnormalities die within the first year of life.
When is an NT scan scheduled during pregnancy?
The clear space in the back of a developing baby’s neck can disappear by week 15, so an NT scan should be completed in the first trimester.
This test can also include blood work to measure your levels of plasma protein and human chorionic gonadotropin (HCG), a maternal hormone. Abnormal levels of either may indicate a chromosome problem.
How does an NT scan work?
During the screening, your doctor or a technician will take an abdominal ultrasound. You could alternatively have a transvaginal test, where an ultrasound probe is inserted through your vagina.
An ultrasound uses high frequency sound waves to create an image from inside your body. From this image, your doctor or technician measures the translucency, or clear space, at the back of your baby’s neck. They can then enter your age or date of birth in a computer program to calculate the risk of your baby having an abnormality.
An NT scan cannot diagnose Down syndrome or any other chromosome abnormality. The test only predicts the risk. Talk to your doctor about available blood tests. They also can help assess your baby’s risk.
As with any prediction, the accuracy rate varies. If you combine an NT scan with blood testing, the screening is about 85 percent accurate for predicting the risk of Down syndrome. If you don’t combine blood testing with the scan, the accuracy rate drops to 75 percent.
No special preparation is required for an NT scan. In most cases, testing is completed in about 30 minutes. During the scan, you’ll lie down on an exam table as the technician moves an ultrasound wand over your stomach.
The ultrasound pictures may be easier to read if you have a full bladder, so your doctor may recommend drinking water about one hour before your appointment. The ultrasound tech needs access to your lower abdomen, so make sure you wear comfortable clothing that makes it accessible.
Results from the scan may be available on the same day of testing, and your doctor may discuss the findings with you before you leave. It’s important to remember that receiving an abnormal result from an NT scan doesn’t necessarily mean that your baby has a chromosome problem. Similarly, normal test results can’t guarantee that your baby won’t be born with Down syndrome.
This test isn’t perfect. There’s a 5 percent false-positive rate. In other words, 5 percent of women tested receive positive results, but the baby is fine. After a positive result, your doctor may suggest another blood test called prenatal cell-free DNA screening. This test examines fetal DNA in your bloodstream to assess your baby’s risk for Down syndrome and other chromosome abnormalities.
Screening vs. diagnostic testing
It can be frightening to receive inconclusive or positive results from an NT scan. Keep in mind that an NT scan can only predict your baby’s risk: It doesn’t offer a definitive answer about chromosomal abnormalities. An NT scan is a screening test, not a diagnostic test.
There are differences between screening and diagnostic testing. The purpose of a screening test is to identify risk factors for a particular disease or condition. Diagnostic testing, on the other hand, confirms the presence of a disease or condition.
How to diagnose an abnormality
To diagnosis a chromosome abnormality, ask your doctor about diagnostic testing. Options include an amniocentesis, which is when a needle is inserted through your stomach into the amniotic sac to retrieve a fluid sample. Amniotic fluid contains cells that provide genetic information about your baby.
Another option is chorionic villus sampling. A sample of your placental tissue is removed and tested for chromosome abnormalities and genetic problems. There’s a small risk of miscarriage with both tests
The takeaway
An NT scan is a safe, noninvasive test that doesn’t cause any harm to you or your baby. Keep in mind that this first trimester screening is recommended, but it’s optional. Some women skip this particular test because they don’t want to know their risk. Talk to your doctor if you experience anxiety, or are worried about how the results might affect you.
Crown Rump Length (CRL) on Ultrasounds
Crown-rump length (CRL) is an ultrasound measurement that is used during pregnancy. The baby measured, in centimeters, from the top of their head (crown) to the bottom of their buttocks (rump).
The limbs and yolk sac are not included in the measurement. The CRL can be measured starting around six or seven weeks of pregnancy up until 14 weeks
What Is Crown-Rump Length?
CRL may be useful in calculating gestational age. With this gestational age, doctors can estimate your potential due date. The earlier the first ultrasound is performed, the more accurate the baby's gestational age will be.
Once the fetus has developed past 14 weeks, head circumference, biparietal diameter, and femur length measurements are used to determine how the baby is progressing.
The length of the umbilical cord is typically the same as the CRL throughout pregnancy.
Uses
Once the fetus's CRL surpasses 7 mm, a heartbeat should be detected by ultrasound. If no heartbeat or cardiac activity is detected, then the pregnancy is likely a missed miscarriage.
A missed, or silent, miscarriage typically occurs without the normal miscarriage symptoms.
The placenta may continue to supply hormones, which can mask the outward signs of a miscarriage.
Women with a mean sac diameter (MSD) of less than 5 mm greater than the CRL are more likely to experience a first-trimester miscarriage even if the baby has a normal heart rate.
Decreased crown-rump length can also diagnose chromosomal anomalies like trisomy 18 (Edwards syndrome) and other trisomies associated with growth restriction.
The embryo and fetus float in the amniotic fluid inside the uterus of the mother usually in a curved posture resembling the letter C. The measurement can actually vary slightly if the fetus is temporarily stretching (straightening) its body. The measurement needs to be in the natural state with an unstretched body which is actually C shaped. The measurement of CRL is useful in determining the gestational age (menstrual age starting from the first day of the last menstrual period) and thus the expected date of delivery (EDD). Different babies do grow at different rates and thus the gestational age is an approximation.
Recent evidence has indicated that CRL growth (and thus the approximation of gestational age) may be influenced by maternal factors such as age, smoking, and folic acid intake. Early in pregnancy gestational age 8 weeks, it is accurate within about +/- 5 days but later in pregnancy due to different growth rates, the accuracy is less. In that situation, other parameters can be used in addition to CRL. The length of the umbilical cord is approximately equal to the CRL throughout pregnancy.
Gestational age is not the same as fertilization age. It takes about 14 days from the first day of the last menstrual period for conception to take place and thus for the conceptus to form. The age from this point in time (conception) is called the fertilization age and is thus 2 weeks shorter than the gestational age.
Thus a 6-week gestational age would be a 4-week fertilization age. Some authorities however casually interchange these terms[citation needed] and the reader is advised to be cautious. An average gestational period (duration of pregnancy from the first day of the last menstrual period up to delivery) is 280 days. On average, this is 9 months and 6 days.
Triple Marker Screen Test
What is a triple marker screen test?
The triple marker screen test is also known as the triple test, multiple marker test, multiple marker screening, and AFP Plus. It analyzes how likely an unborn baby is to have certain genetic disorders. The exam measures the levels of three important substances in the placenta:
- alpha-fetoprotein (AFP)
- human chorionic gonadotropin (HCG)
- Estriol
Triple marker screening is administered as a blood test. It’s used for women who are between 15 and 20 weeks pregnant. An alternative to this test is the quadruple marker screen test, which also looks at a substance called inhibin A.
What does a triple marker screen test do?
A triple marker screen test takes a sample of blood and detects the levels of AFP, HCG, and estriol in it.
AFP: A protein produced by the fetus. High levels of this protein can indicate certain potential defects, such as neural tube defects or failure of the fetus’s abdomen to close.
HGC: A hormone produced by the placenta. Low levels may indicate potential problems with the pregnancy, including possible miscarriage or ectopic pregnancy. High levels of HGC can indicate a molar pregnancy, or a multiple pregnancy with two or more children.
Estriol: An estrogen that comes from both the fetus and the placenta. Low estriol levels may indicate risk of having a baby with Down syndrome, especially when paired with low AFP levels and high HGC levels.
Abnormal levels
Abnormal levels of these substances may indicate the presence of:
- neural tube defects, such as spina bifida and anencephaly
- multiple infants, such as twins or triplets
- an improper timeline, where the pregnancy is further along or not as far along as once thought
Abnormal levels can also indicate Down syndrome or Edwards syndrome. Down syndrome occurs when the fetus develops an extra copy of chromosome 21. It can cause medical problems and, in some cases, learning disabilities. Edwards syndrome can result in extensive medical complications. These are sometimes life-threatening in the first months and years after birth. Only 50 percent of fetuses with this condition survive to birth, according to the Trisomy 18 Foundation.
Who benefits from the triple marker screen test?
Triple marker screen tests help prospective parents prepare and assess options. They also alert doctors to watch a fetus more closely for other signs of complications.
The test is often most recommended for women who:
- are 35 years old or older
- have a family history of birth defects
- have diabetes and use insulin
- have been exposed to high levels of radiation
- had a viral infection during pregnancy
What are the results of a triple marker screen test?
The results of the triple marker screen test show the likelihood of an infant having a genetic disorder such as Down syndrome or spina bifida. Test results aren’t infallible. They merely show a probability, and may be an indication for additional testing.
Doctors often consider several other factors that can affect the test results. These include:
· the mother’s weight
· her ethnicity
· her age
· whether or not she has diabetes
· how far along the she is in her pregnancy
· whether or not she’s having a multiple pregnancy
Next steps
Parents who receive negative indicators on their triple marker screen test must then decide what actions to take. While abnormal results can be concerning, they don’t necessarily mean that there’s anything to worry about yet. Instead, they’re a good indication to explore further testing or monitoring.
In the case of abnormal results, an amniocentesis test may be ordered. In this test, a sample of amniotic fluid is taken from the uterus via a thin, hollow needle. This test can help detect genetic conditions and fetal infections.
If your results show high levels of AFP, your doctor will likely order a detailed ultrasound to examine the fetal skull and spine for neural tube defects.
Ultrasounds can also help determine the age of the fetus and how many fetuses a woman is carrying.
The Quad Screen Test: What You Need to Know
The quad what?
The quad screen — also called the maternal serum screen — is a prenatal screening test that analyzes four substances in your blood. (Thank Latin for that — quad means four.) It’s usually carried out between your 15th and 22nd week of pregnancy.
The quad screen can tell you if your baby has an increased chance of:
· Down syndrome
· trisomy 18 (Edwards Syndrome)
· neural tube defects
· abdominal wall defects
It does so in part by measuring these four substances:
· alpha-fetoprotein (AFP), a protein produced by your baby’s liver
· human chorionic gonadotropin (hCG), a hormone produced by your placenta
· Estriol (uE3): a hormone made by your placenta and the baby’s liver. Estriol is the highest amount of circulating hormone in a woman’s blood while she’s pregnant. Low levels of this hormone are associated with increased risk for Down syndrome and trisomy 18.
· inhibin A, a third hormone produced by your placenta. Doctors don’t know exactly the role this protein plays in pregnancy. But they do know that it increases the reliability of the sequential screening test. High levels are associated with Down syndrome while low levels are associated with trisomy 18.
Yup, pregnancy is a heavy hormone-production 9 months. Now you can stop wondering why you’ve been feeling so tired!
Should you get the quad screen test?
This is an optional test, which means you don’t have to do it. But many doctors recommend it for all pregnant women. Here’s what might make you opt in:
· You’re 35 or older. Since the test is noninvasive, if you’re worried about your baby’s health only because of your age, this test is a good option.
· Your family has a history of developmental irregularities at birth (e.g., spina bifida, cleft palate).
· You’ve already had a child with developmental irregularities at birth.
· You have type 1 diabetes.
Keep in mind that the quad screen doesn’t just look at the results of your blood test. It adds in different factors — such as your age, ethnicity, and weight — and then estimates the chances that your baby may have an abnormality.
The screen doesn’t tell you that there’s definitely a problem; if abnormal, it tells you that you should have further testing.
How the results are determined
By now, you’ve realized that each week of pregnancy is different than the week before. (The 10 jars of pickles you asked for last week are now probably being used as door stoppers.) That means that the levels of AFP, hCG, estriol, and inhibin A in your blood are also changing week by week.
That’s why it’s important to make sure you’ve told your OB how far along you are in your pregnancy. By using an automated analyzer and a software package, doctors can screen your blood and calculate the chances of serious disorders.
What the results mean
Want to take a deep breath before we look at what the results could mean? You’re right, thinking about these conditions can be downright scary. However, even if your quad screen is positive (meaning that there are higher chances that your baby could have one of these conditions), it doesn’t necessarily mean that your baby will be affected. It just means that the chances are higher.
If you’re thinking, “Huh?” here’s an example: About 4 percent of quad screens will return positive for an increased risk of Down syndrome, but only about 1 to 2 percent of those babies will have Down syndrome. Breathe out now.
Let’s skirt round the exact numbers and get to the nitty gritty according to the Cleveland Clinic:
· Higher than normal AFP levels could mean that your baby has an open neural tube defect such as spina bifida or anencephaly. On the other hand, they could also mean that he’s older than you thought or that — guess what — you’re expecting twins.
· Lower than normal AFP, hCG, and inhibin A levels could mean that you have higher chances of having a baby with Down syndrome or trisomy 18.
· Lower than normal levels of estriol may also mean that you have higher chances of having a baby with Down syndrome or trisomy 18.
More on the conditions
· Down syndrome is a genetic condition that comes from extra genetic material (the 21st chromosome). Approximately 1 in 700 babies is born with Down syndrome.
· Trisomy 18 is a genetic condition that comes from extra chromosome number 18. Most trisomy 18 pregnancies result in miscarriages or stillbirth; babies who are born, live for only a few years. About 1 in 5,000 babies is born with this condition.
· Neural tube defects include conditions like spina bifida or anencephaly. Spina bifida is when the brain, spinal cord, or the spinal cord’s protective covering doesn’t develop properly. Anencephaly means that the baby’s brain doesn’t form completely. Neural tube defects occur in 1 or 2 out of every 1,000 births.
How accurate is the quad screen test?
· The test can detect approximately 75 percent of Down syndrome cases in women under age 35 and 85 to 90 percent of Down syndrome cases in women age 35 years and older. Remember, though, that most people who are told they have an increased risk of having a Down syndrome baby don’t end up having a baby with Down syndrome.
· It can also detect approximately 75 percent of open neural tube defects.
· If the quad screen test is negative, there’s still a possibility that your baby could be born with one of these conditions.
Further testing after a positive quad screen test
What happens if you have a positive quad screen test? First, remember that many women who show positive test results go on to have babies that are just fine.
The next step is a consultation with a genetic counselor, and together you’ll decide whether further testing is right for you. Sometimes this means another quad screen test and a high definition (targeted) ultrasound. And then, if the results are still positive, you may want to do the following tests:
· Prenatal cell-free DNA screening. This blood test examines cell-free DNA coming from your placenta and your baby and found in your bloodstream.
· Chorionic villus sampling (CVS). A sample of tissue from the placenta is removed for testing.
· Amniocentesis. A sample of amniotic fluid is drawn for testing.
The downside here is that both CVS and amniocentesis pose a slight threat for miscarriage.
NIPT (Noninvasive Prenatal Testing)
Explaining the NIPT screen
The NIPT prenatal test is sometimes called the noninvasive prenatal screen (NIPS). By 10 weeks of pregnancy, your healthcare provider may talk to you about this elective test as an option to help identify if your baby is at risk for genetic abnormalities, such as chromosomal disorders.
Most commonly, the test determines the risk of disorders such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13), as well as conditions caused by missing or extra X and Y chromosomes.
The blood test looks at tiny pieces of cell-free DNA (cfDNA) from the placenta that are present in a pregnant woman’s blood. cfDNA is created when these cells die and are broken down, releasing some DNA into the bloodstream.
It’s important to know that NIPT is a screening test — not a diagnostic test. This means that it can’t diagnose a genetic condition with certainty. It can, however, predict whether the risk of a genetic condition is high or low.
On the positive side, cfDNA also holds the answer to a big question: whether you’re carrying a boy or a girl. Yes, this prenatal test can reveal your baby’s sex in the first trimester — earlier than any ultrasound!
Who should get the NIPT prenatal test
While optional, the NIPT is usually offered to women based on her OB-GYN or midwife’s recommendations and protocols. However, there are some risk factors that might lead your providers to more strongly recommend it.
According to this 2013 review of the NIPT, some of these risk factors include:
- maternal age of 35 and older at delivery
- a personal or family history of a pregnancy with a chromosomal abnormality
- a maternal or paternal chromosomal abnormality
Deciding to have the NIPT screening is a very personal decision, so it’s OK to take the time you need to determine what’s best for you. If you’re having a difficult time, consider speaking to your healthcare provider or a genetic counselor who can help address your concerns and better inform you.
Understanding what the NIPT test results mean
The NIPT measures the fetal cfDNA in the mother’s bloodstream, which comes from the placenta. This is called the fetal fraction. For the most accurate test results possible, the fetal fraction must be over 4 percent. This usually happens around the 10th week of pregnancy and this is why the test is recommended after this time.
There are several ways the fetal cfDNA can be analyzed. The most common way is to determine the amount of both maternal and fetal cfDNA. The test will look at specific chromosomes to see if the percentage of cfDNA from each of these chromosomes is considered “normal.”
If it falls within the standard range, the result will be “negative.” This means the fetus has a decreased risk of the genetic conditions caused by the chromosomes in question.
If the cfDNA is more than the standard range, this could lead to a “positive” result, meaning the fetus may have an increased risk of a genetic condition. But please be reassured of this: NIPT is not 100 percent conclusive. Positive results require further testing to confirm any true-positive fetal chromosomal abnormality or related disorder.
We do also have to mention that there is also a very low risk of getting a false negative NIPT result. In this case, a baby could be born with a genetic abnormality that was not detected with the NIPT or additional screenings throughout the course of pregnancy.
How accurate is the NIPT?
According to this 2016 study, NIPT has a very high sensitivity (true positive rate) and specificity (true negative rate) for Down syndrome. For other conditions such as Edwards and Patau syndrome, the sensitivity is slightly lower but still strong.
It’s important to reiterate, however, that the test is not 100 percent accurate or diagnostic.
In this 2016 study on false negative NIPT results, it was determined that for every 1 in 426 samples of people at high risk for common chromosomal abnormalities, a trisomy 18 (Edwards syndrome) or trisomy 21 (Down syndrome) is undiagnosed due to specific biological differences within the chromosome itself.
False positive NIPT screening results can happen as well. If you have a positive NIPT result, your healthcare provider will likely order additional diagnostic tests. In some cases, these diagnostic tests reveal that the baby doesn’t have a chromosomal abnormality after all.
Additional genetic testing
If your NIPT screening tests come back positive, your OB-GYN or midwife might recommend additional diagnostic genetic tests, as outlined by this 2013 article. Some of these tests are more invasive, including prenatal chorionic villus sampling (CVS) and amniocentesis.
The CVS test takes a small sample of cells from the placenta, whereas amniocentesis takes a sample of amniotic fluid. Both tests can determine if the fetus has any chromosomal abnormalities with more diagnostic certainty.
Because these two tests can bring the small risk of a miscarriage, they’re recommended selectively and cautiously based on the collaborative decision between you and your medical team.
That said, there are additional noninvasive screenings that might be suggested, including the first trimester risk assessment usually done at 11 to 14 weeks, the quad screening at 15 to 20 weeks, and at 18 to 22 weeks, the fetal structural survey performed via ultrasound
Amniocentesis
Amniocentesis is a procedure in which your doctor removes a small amount of amniotic fluid from your uterus. The amount of fluid removed is typically no more than 1 ounce.
Amniotic fluid surrounds your baby in the womb. This fluid contains some of your baby’s cells and is used to find out if your baby has any genetic abnormalities. This type of amniocentesis is usually performed in the second trimester, typically after week 15.
It can also be used to determine if your baby’s lungs are mature enough to survive outside the womb. This type of amniocentesis would occur later in your pregnancy.
Your doctor will use a long, thin needle to collect a small amount of amniotic fluid. This fluid surrounds and protects the baby while they’re in your womb.
A laboratory technician will then test the fluid for certain genetic disorders, including Down syndrome, spina bifida, and cystic fibrosis.
The test results can help you make decisions about your pregnancy. In the third trimester, the test can also tell you whether or not your baby is mature enough to be born.
It’s also helpful for determining whether you need to deliver early to prevent complications from your pregnancy.
Why is amniocentesis recommended?
Abnormal prenatal screening test results are one common reason you might consider amniocentesis. Amniocentesis can help your doctor confirm or deny any indications of abnormalities found during the screening test.
If you’ve already had a child with a birth defect or a serious abnormality of the brain or spinal cord called a neural tube defect, amniocentesis can check whether your unborn child also has the condition.
If you’re 35 years or older, your baby is at a higher risk for chromosomal abnormalities, such as Down syndrome. Amniocentesis can identify these abnormalities.
If you or your partner is a known carrier of a genetic disorder, such as cystic fibrosis, amniocentesis can detect whether your unborn child has this disorder.
Complications during pregnancy might require you to deliver your baby earlier than the full term. A maturity amniocentesis can help determine if your baby’s lungs are mature enough to allow your child to survive outside of the womb.
Your doctor may also recommend an amniocentesis if they suspect that your unborn child has an infection or anemia or they think you have a uterine infection.
If it’s necessary, the procedure can also be done to decrease the amount of amniotic fluid in your womb.
How is amniocentesis performed?
This test is an outpatient procedure, so you won’t need to stay in the hospital. Your doctor will first perform an ultrasound to determine the exact location of your baby in your uterus.
An ultrasound is a noninvasive procedure that uses high-frequency sound waves to create an image of your unborn baby. Your bladder must be full during the ultrasound, so drink plenty of fluids beforehand.
After the ultrasound, your doctor may apply numbing medication to an area of your belly. The ultrasound results will give them a safe location to insert the needle.
Then, they’ll insert a needle through your belly and into your womb, withdrawing a small amount of amniotic fluid. This portion of the procedure usually takes about 2 minutes.
The results of genetic tests on your amniotic fluid are usually available within a few days.
The results of tests to determine the maturity of your baby’s lungs are usually available within a few hours.
What are the complications associated with amniocentesis?
Amniocentesis is usually recommended between 16 to 20 weeks, which is during your second trimester. Although complications can occur, it’s rare to experience the more severe ones.
The risk of miscarriage is up to .3 percent if you have the procedure during the second trimester, according to the Mayo Clinic. The risk is slightly higher if the test occurs before 15 weeks of pregnancy.
Complications associated with amniocentesis include the following:
· cramps
· a small amount of vaginal bleeding
· amniotic fluid that leaks out of the body (this is rare)
· uterine infection (also rare)
Amniocentesis can cause infections, such as hepatitis C or HIV, to transfer to the unborn baby.
In rare cases, this test may cause some of your baby’s blood cells to enter your bloodstream. This is important because there’s a type of protein called the Rh factor. If you have this protein, your blood is Rh-positive.
If you don’t have this protein, your blood is Rh-negative. It’s possible for you and your baby to have different Rh classifications. If this is the case and your blood mixes with your baby’s blood, your body may react as if it were allergic to your baby’s blood.
If this happens, your doctor will give you a drug called RhoGAM. This medication will prevent your body from making antibodies that will attack your baby’s blood cells.
What do the test results mean?
If the results of your amniocentesis are normal, your baby most likely doesn’t have genetic or chromosomal abnormalities.
In the case of maturity amniocentesis, normal test results will assure you that your baby is ready to be born with a high likelihood for survival.
Abnormal results may mean there’s a genetic problem or chromosomal abnormality. But that doesn’t mean it’s absolute. Additional diagnostic tests can be done to get more information.
Down Syndrome
What is Down syndrome?
Down syndrome (sometimes called Down’s syndrome) is a condition in which a child is born with an extra copy of their 21st chromosome — hence its other name, trisomy 21. This causes physical and mental developmental delays and disabilities.
Many of the disabilities are lifelong, and they can also shorten life expectancy. However, people with Down syndrome can live healthy and fulfilling lives. Recent medical advances, as well as cultural and institutional support for people with Down syndrome and their families, provides many opportunities to help overcome the challenges of this condition.
In all cases of reproduction, both parents pass their genes on to their children. These genes are carried in chromosomes. When the baby’s cells develop, each cell is supposed to receive 23 pairs of chromosomes, for 46 chromosomes total. Half of the chromosomes are from the mother, and half are from the father.
In children with Down syndrome, one of the chromosomes doesn’t separate properly. The baby ends up with three copies, or an extra partial copy, of chromosome 21, instead of two. This extra chromosome causes problems as the brain and physical features develop.
According to the National Down Syndrome Society (NDSS), about 1 in 700 babies in the United States is born with Down syndrome. It’s the most common genetic disorder in the United States.
Types of Down syndrome
There are three types of Down syndrome:
Trisomy 21
Trisomy 21 means there’s an extra copy of chromosome 21 in every cell. This is the most common form of Down syndrome.
Mosaicism
Mosaicism occurs when a child is born with an extra chromosome in some but not all of their cells. People with mosaic Down syndrome tend to have fewer symptoms than those with trisomy 21.
Translocation
In this type of Down syndrome, children have only an extra part of chromosome 21. There are 46 total chromosomes. However, one of them has an extra piece of chromosome 21 attached.
Will my child have Down syndrome?
Certain parents have a greater chance of giving birth to a child with Down syndrome. According to the Centers for Disease and Prevention, mothers aged 35 and older are more likely to have a baby with Down syndrome than younger mothers. The probability increases the older the mother is.
Research shows that paternal age also has an effect. One 2003 study found that fathers over 40 had twice the chance of having a child with Down syndrome.
Other parents who are more likely to have a child with Down syndrome include:
- people with a family history of Down syndrome
- people who carry the genetic translocation
It’s important to remember that no one of these factors mean that you’ll definitely have a baby with Down syndrome. However, statistically and over a large population, they may increase the chance that you may.
What are the symptoms of Down syndrome?
Though the likelihood of carrying a baby with Down syndrome can be estimated by screening during pregnancy, you won’t experience any symptoms of carrying a child with Down syndrome.
At birth, babies with Down syndrome usually have certain characteristic signs, including:
· flat facial features
· small head and ears
· short neck
· bulging tongue
· eyes that slant upward
· atypically shaped ears
· poor muscle tone
An infant with Down syndrome can be born an average size, but will develop more slowly than a child without the condition.
People with Down syndrome usually have some degree of developmental disability, but it’s often mild to moderate. Mental and social development delays may mean that the child could have:
- impulsive behavior
- poor judgment
- short attention span
- slow learning capabilities
Medical complications often accompany Down syndrome. These may include:
- congenital heart defects
- hearing loss
- poor vision
- cataracts (clouded eyes)
- hip problems, such as dislocations
- leukemia
- chronic constipation
- sleep apnea (interrupted breathing during sleep)
- dementia (thought and memory problems)
- hypothyroidism (low thyroid function)
- obesity
- late tooth growth, causing problems with chewing
- Alzheimer’s disease later in life
People with Down syndrome are also more prone to infection. They may struggle with respiratory infections, urinary tract infections, and skin infections.
Screening for Down syndrome during pregnancy
Screening for Down syndrome is offered as a routine part of prenatal care in the United States. If you’re a woman over 35, your baby’s father is over 40, or there’s a family history of Down syndrome, you may want to get an evaluation.
First trimester
An ultrasound evaluation and blood tests can look for Down syndrome in your fetus. These tests have a higher false-positive rate than tests done at later pregnancy stages. If results aren’t normal, your doctor may follow up with an amniocentesis after your 15th week of pregnancy.
Second trimester
An ultrasound and quadruple marker screen (QMS) test can help identify Down syndrome and other defects in the brain and spinal cord. This test is done between 15 and 20 weeks of pregnancy.
If any of these tests aren’t normal, you’ll be considered at high risk for birth defects.
Additional prenatal tests
Your doctor may order additional tests to detect Down syndrome in your baby. These may include:
· Amniocentesis. Your doctor takes a sample of amniotic fluid to examine the number of chromosomes your baby has. The test is usually done after 15 weeks.
· Chorionic villus sampling (CVS). Your doctor will take cells from your placenta to analyze fetal chromosomes. This test is done between the 9th and 14th week of pregnancy. It can increase your risk of a miscarriage, but according to the Mayo Clinic, only by less than 1 percent.
· Percutaneous umbilical blood sampling (PUBS, or cordocentesis). Your doctor will take blood from the umbilical cord and examine it for chromosomal defects. It’s done after the 18th week of pregnancy. It has a higher risk of miscarriage, so it’s performed only if all other tests are uncertain.
Some women choose not to undergo these tests because of the risk of miscarriage. They’d rather have a child with Down syndrome than lose the pregnancy.
Tests at birth
At birth, your doctor will:
- perform a physical examination of your baby
- order a blood test called a karyotype to confirm Down syndrome
Treating Down syndrome
There’s no cure for Down syndrome, but there’s a wide variety of support and educational programs that can help both people with the condition and their families.
Available programs start with interventions in infancy. Federal law requires that states offer therapy programs for qualifying families. In these programs, special education teachers and therapists will help your child learn:
· sensory skills
· social skills
· self-help skills
· motor skills
· language and cognitive abilities
Children with Down syndrome often meet age-related milestones. However, they may learn more slowly than other children.
School is an important part of the life of a child with Down syndrome, regardless of intellectual ability. Public and private schools support people with Down syndrome and their families with integrated classrooms and special education opportunities. Schooling allows valuable socialization and helps students with Down syndrome build important life skills.
The lifespan for people with Down syndrome has improved dramatically in recent decades. In 1960, a baby born with Down syndrome often didn’t see their 10th birthday. Today, life expectancy for people with Down syndrome has reached an average of 50 to 60 years.
If you’re raising a child with Down syndrome, you’ll need a close relationship with medical professionals who understand the condition’s unique challenges. In addition to larger concerns — like heart defects and leukemia — people with Down syndrome may need to be guarded from common infections such as colds.
People with Down syndrome are living longer and richer lives now more than ever. Though they can often face a unique set of challenges, they can also overcome those obstacles and thrive. Building a strong support network of experienced professionals and understanding family and friends is crucial for the success of people with Down syndrome and their families.
What Is Trisomy 18 or Edwards Syndrome?
Did you know that your baby’s genetic makeup was determined at conception? From the moment the sperm met the egg, your little one’s genetic code — DNA — began forming. It’s made up of 23 pairs of chromosomes. Sometimes, though, extra chromosomes make their way into the mix and can result in something called a trisomy.
Edwards syndrome is also known as trisomy 18. It means a person has an extra copy of chromosome number 18, leading to issues with development. Here’s more about the symptoms of this syndrome, what causes it, and what you might expect after a diagnosis.
What is trisomy 18?
Trisomy 18 is a rare genetic disorder that affects approximately 1 in every 3,315 births in the United States — around 1,187 babies each year.
In typical development, a baby gets 23 pairs of chromosomes from its parents during conception — 22 are called autosomes, and 1 set is made up of sex chromosomes (X and/or Y, depending on the baby’s sex).
The word “trisomy” means three bodies. When there are three copies of the chromosome versus the usual two, it creates an imbalance. As a result, a baby may be born with certain structural changes some of which may lead to miscarriage, stillbirth, or death after the baby is born.
Variations
Babies can be born with an extra copy of chromosome 18 in each cell in the body. This is called complete trisomy 18 and causes more serious health outcomes.
Mosaic trisomy 18 happens when only some cells in the body contain the extra chromosome. Around 5 percent of babies with trisomy 18 have the mosaic form. This generally leads to milder irregularities and longer life expectancy.
Partial trisomy 18 happens when an extra copy of chromosome 18 attaches to another chromosome. Again, the severity of the syndrome tends to be associated with the total number of cells affected by the trisomy. So, a partial trisomy tends to have less severe effects and longer life expectancy.
What are the symptoms of trisomy 18?
You may not notice anything different in your pregnancy if your baby has Edwards syndrome. In fact, you may not learn about your baby’s diagnosis until after your doctor orders certain prenatal screening tests, like:
· cell-free DNA screening
· ultrasound
· amniocentesis
Some families do not discover their child’s diagnosis until birth, when the following physical features may include:
· low birth weight
· low muscle tone
· smaller head
· wide-set eyes
· small lower jaw
· cleft lip or palate
· webbed neck
· hand issues, like clenched first or second and fifth fingers on top of other fingers
· rocker bottom feet
· crossed legs
· shortened breastbone
Other health issues may include:
· feeding or sucking difficulties
· trouble gaining weight (also known as failure to thrive)
· congenital heart issues, like ventricular septal defect
· cryptorchidism — undescended testicles
· eye or vision issues, like clouding of the corneas, small eyes, strabismus (crossed eyes), or nystagmus (uncontrolled eye movements)
· hearing loss
· seizures
· gastrointestinal issues
· cancerous tumors, particularly in the kidneys and liver
What causes trisomy 18?
Trisomy 18 is caused by any situation that leads to an extra copy of chromosome 18 in the body.
In most cases, it happens when the sperm meets the egg during conception. In one scenario, the reproductive material of either parent may spontaneously divide. In another, the trisomy may happen as cells divide after fertilization. Whatever the case, the extra chromosome happens at random.
Translocation is another possibility, which means that parts of chromosomes break off and attach to other chromosomes. This may happen randomly or through a “balanced” translocation, in which one parent has a set of chromosomes that aren’t typical but are balanced. When chromosomes are balanced, they don’t cause medical issues. After reproduction, though, genetic information passed on may cause a trisomy.
How is trisomy 18 diagnosed?
Edwards syndrome may be diagnosed at some point during your pregnancy. You may have a cell-free DNA screening (cfDNA) at any time after 10 weeks of pregnancy and until delivery. cfDNA is a simple blood test that screens for genetic conditions. A positive result on this test means you’ll need further testing to confirm the results.
Other tests during pregnancy include.
· Amniocentesis and chorionic villus sampling are more invasive diagnostic tools you may get after 15 weeks of pregnancy. Your doctor will take a sample of your amniotic fluid or placenta to look for extra copies of chromosome 18.
· An ultrasound exam may uncover physical features (small head, webbed neck, hand or foot irregularities, etc.) of the syndrome.
Other times, trisomy 18 may not be diagnosed until after your baby is born. Your child’s doctor may diagnose it based on:
· physical features or characteristics
· heart issues or other defects
· blood tests that analyze your child’s chromosomes
What is the treatment for trisomy 18?
There is no cure for trisomy 18. Since babies with this condition tend to have multiple health issues, you’ll work with a team of doctors to create a customized treatment plan. In more severe cases, some families favor palliative care or hospice care.
Treatments are more about making a child comfortable or correcting the issues that affect an individual child. For example, surgery may be an option to treat things like:
· heart defects
· kidney issues
· head or face irregularities
As a child grows, they may need support academically and physically. Early intervention and special education programs can help fill these gaps.
What are the risk factors for trisomy 18?
You may be surprised to learn that there are very few risk factors for Edwards syndrome.
There may be an increased chance of having a baby with a trisomy as you get older. While different reports show mothers in their late teens and 20s can have children with trisomy 18, the mean age is closer to 32.5 years old.
In rare cases, trisomy 18 may be inherited from a biological parent (through balanced translocation). If you already have had one child with a trisomy, your doctor may suggest getting genetic testing to assess your chances of having another child with a similar condition.
The vast majority of the time, though, Edwards syndrome happens by chance during conception when the sperm meets the egg.
What’s the outlook for people with trisomy 18?
It’s important to be prepared for all possibilities with a condition like trisomy 18. Researchers share that nearly half of all babies born with Edwards syndrome who survive delivery may not live beyond the first week of life.
That said, the severity of the syndrome depends on the type (complete, mosaic, partial, etc.) and whatever effects it has on your individual child. All children are different, and all outlooks will be unique as a result.
Of children born with Edwards syndrome, nearly 50 percent will not survive beyond the first week of life. However, around 10 percent will reach their first birthday, and some may live to their teen years or even adulthood, but they will need medical support or therapies, including:
· physical therapy
· occupational therapy
· speech therapy
What Is Trisomy 13 or Patau Syndrome?
A baby’s genetic makeup is determined when the sperm meets the egg during fertilization. Typically, a full set of DNA is formed, which contains 23 pairs of chromosomes. Sometimes, extra chromosomes are shared, resulting in what is called a trisomy.
Patau syndrome is also known as trisomy 13. It means that a person has an extra copy of chromosome number 13.
What is trisomy 13?
Trisomy 13 is a rare genetic disorder that affects around 1 in every 7,409 births in the United States. It is present when there are three copies of chromosome 13 instead of the usual two in each cell in the body.
While rare, trisomy 13 is a very serious condition that can cause developmental issues that may lead to miscarriage, stillbirth, or infant death soon after birth.
A child who does survive may have a low birth weight and other serious medical issues.
Variations
If there is a complete extra copy of chromosome number 13 in each cell, the condition is called trisomy 13.
Sometimes this extra genetic information gets split between chromosome 13 and another chromosome — a translocation. This happens about 10 percent of the time.
In about 5 percent of individuals with trisomy 13, the extra copy of chromosome 13 only affects some cells and not all. When this happens, it’s called trisomy 13 mosaicism or partial trisomy 13. For individuals with mosaic trisomy 13, the signs and symptoms are generally less severe, and children may live longer.
What are the symptoms of trisomy 13?
You may have no symptoms during your pregnancy that indicate your child has Patau syndrome. Your doctor may uncover the first signs after cell-free DNA screening, other prenatal screening tests, or during a routine ultrasound exam.
Once your baby is born, you may observe the following features:
· low birth weight, problems with feeding, and low muscle tone
· microcephaly (small head) and face/head issues, like skin missing on the scalp, ear malformation, or capillary hemangiomas (raised birthmarks)
· microphthalmia (small eyes), anophthalmia (missing one or both eyes), or hypotelorism (eyes spaced closely together)
· cleft lip and palate
· polydactyly (extra fingers or toes)
· small penis or enlarged clitoris
· seizures
· apnea
· deafness
Around 80 percent of babies born with trisomy 13 also have congenital heart abnormalities. Some may also have conditions that affect brain development and the kidneys.
What causes trisomy 13?
In most cases, trisomy 13 happens spontaneously soon after the sperm and egg meet. The issue may arise as the reproductive material of either parent divides, or it may happen as cells divide after fertilization itself. In either of these cases, the extra chromosome happens at random.
That said, in rare cases, some people may pass a trisomy onto their child if they themselves have what is called a “balanced” translocation. This means that the parent carrier has a set of chromosomes that aren’t the norm but that they are balanced, so they don’t cause medical issues. However, when the parent with the balanced translocation has a child, the genetic information may be passed on and cause a trisomy 13 in the child.
How is trisomy 13 diagnosed?
Trisomy 13 can be diagnosed while you are pregnant or after your baby is born.
· A cell-free DNA screening is a noninvasive blood test that can be done as early as 10 weeks into pregnancy. If your screen shows a positive result, it means that your child may have trisomy 13, but that more concrete testing is needed.
· An ultrasound scan may reveal certain features that match up with Patau syndrome, like extra fingers or toes, small head size, or eye abnormalities.
· Amniocentesis is a diagnostic test that can be done after week 15 of pregnancy. Your doctor will obtain a sample of amniotic fluid to look for additional chromosomes.
· Chorionic villus sampling is a test that can be done earlier than amniocentesis, at 10 to 13 weeks. Your doctor will obtain a sample of placental tissue to look for additional chromosomes.
After birth, your child’s doctor may make a diagnosis based on a physical exam, certain characteristics, and blood tests to analyze chromosomes.
What is the treatment for trisomy 13?
Treatment for Patau syndrome is often targeted at whatever symptoms a child is experiencing. Instead of curative treatments, medical help tends to be focused on making the child comfortable, since many babies do not live long after birth.
Your doctor may assemble a healthcare team to provide care for various health conditions while working together. Treatments may eventually involve surgery — for heart issues, cleft palate or lip, or other conditions — physical therapy, and other medical or social services.
Children who live longer may also benefit from early intervention and special education programs as they grow.
What are the risk factors for trisomy 13?
Since most cases of Patau syndrome happen at random, it’s possible to have a child with this condition even if you have no known risk factors.
The primary risk factor mentioned in the medical literature is paternal age. So, as a parent’s age goes up, so does the potential for trisomy 13.
Again, the other risk factor is if either parent has a “balanced” translocation. This can be uncovered through genetic testing.
Your doctor may also suggest genetic testing if you already have a child with trisomy 13 (or another genetic condition) to determine if there’s an inherited factor at play that may impact future pregnancies.
What is the outlook for people with trisomy 13?
Trisomy 13 is a very serious but very rare condition. About half of all pregnancies involving trisomy 13 will result in pregnancy loss before the 12th week. According to a 2017 study, 84 percent of pregnancies involving trisomy 13 that reach 39 weeks result in a live birth.
However, more than 90 percent of infants with trisomy 13 will not survive their first year. Most babies with this rare condition live only 7 to 10 days.
Around 5 percent of children with trisomy 13 will live beyond the first year, though they will likely have growth and developmental delays.
Some children with trisomy 13 may live longer, but this is extremely rare.
Neural Tube Birth Defect in Babies
During the early stages of pregnancy, the core structure that develops into the baby’s spinal cord and brain are formed. Due to some deficiencies and genetic factors, some foetuses develop these structures with some abnormality. These abnormalities stay and get magnified as defects in the brain or spinal cord. These malformations are collectively called neural tube defects (NTD). This article discusses the various aspects of this birth defect, and the precautions that expecting mothers can take to deliver a healthy baby.
What Are Neural Tube Defects?
Neural tube defects are birth defects that are characterized by abnormalities in the spine or brain of the developing foetus. It is one of the most common forms of birth defects in babies worldwide. These defects occur during the first month of the pregnancy, and are detected in the first trimester itself.
What Is a Neural Tube?
The neural tube is a flat and tiny ribbon-shaped structure that develops inside an embryo within the first few weeks of its formation. It is this primitive structure that gives rise to the brain and the spinal cord in a fully developed baby. As this structure forms the basis of the vital organs, an abnormality in its development or differentiation results in a group of defects termed as neural tube defects.
Types of Neural Tube Defects
Neural tube defects are broadly classified as open neural tube defects and closed neural tube defects, based on the whether the brain and spinal cord are covered or not. Each of these has a number of subtypes, which are discussed in detail below.
Open Type Neural Tube Defects
In the open type neural defect, the brain and the spinal cord are seen outside the skull or the vertebral column. Meningitis is commonly found to be associated with this type of defect. The open type includes conditions like spina bifida, encephaloceles, iniencephaly, and schizencephaly, hydranencephaly, and anencephaly.
1. Spina Bifida
Spina bifida is a very common type of neural tube defect that is caused when the lower part of the spinal cord protrudes out of the body. It is usually associated with damaged nerves in that region. Children with spina bifida are likely to have paralysis of the extremities, especially the leg, and poor control of urine and stool.
There are three sub-types of spina bifida, namely, spina bifida occulta, meningocele, and myelomeningocele. Spina bifida occulta is the mildest form of spina bifida, where there is a small space in the spinal cord that does not have any implications on the brain or spinal cord. Meningocele is a condition that refers to a small protrusion of the meninges in the back. Myelomeningocele is a very severe form of the neural tube defect that involves the protrusion of a small portion of the spinal cord and the surrounding tissue. It is characterised by intellectual disability caused by fluid accumulation in the brain, and complete or partial paralysis of the leg.
2. Anencephaly
Anencephaly is the abnormality of the neural tube in the upper end, causing children to be born without a portion of the brain and the skull. The remaining part of the brain is very cluttered and disorganised. Children with anencephaly are usually still born or do not survive for more than a few weeks of birth.
3. Encephalocely
During the formation of brain in the embryo, when the neural tube does not close properly, leaving a sac-like protrusion of the brain and its membrane, it is termed as encephalocele. This condition is relatively rare, and is almost always accompanied by developmental disabilities, paralysis of the upper and lower extremities, seizures, hydrocephalus, ataxia, abnormalities of the face and head, and problems wit vision. Some children who have encephalocele survive to have normal intelligence.
4. Iniencephaly
Iniencephaly is a rare form of a neural tube defect that is characterised by exceptionally large heads that are tilted backwards. It is also often associated with absence of neck, distorted spine, defective spinal cord, and cleft lip. Babies born with this disorder do not survive for long after birth.
Closed Type Neural Tube Defects
In the closed neural tube defect, the neural tissue is not visible outside. It is covered by a patch of hairy or discloured skin. In this type of neural defect, the spinal cord is attached to the tissue of the back, preventing it from growing with age. Some types of closed neural tube defects are:
1. Lipomyelomeningocele
This is a condition where a mass of fat tissue under the skin tethers itself to the back bone, preventing it from growing. It is visible as a large lump, and is often associated with poor bladder and bowel control, and weakness in the legs.
2. Lipomeningocele
Lipomeningocele is a condition where a small portion of the spinal cord protrudes out under the skin, and gets attached to the tissues in the back. The protrusion affects the nerves radiating from that part of the spinal cord, giving raise to neurological defects.
Causes
The causes of neural tube defects can be one of the following:
Genetic Factors
Neural tube defects are caused due to certain mutations in genes encoding the enzyme Methylenetetrahydrofolate reductase (MTHFR). These variations can increase the likelihood of a child being born with neural defects. A family history of tube defects also increases the chances greatly.
Folic Acid Deficiency
Folic acid, or Vitamin B9, is an absolutely vital nutrient for the proper formation of the neural tube. Expecting mothers who have a deficiency of folic acid have a higher chance of giving birth to a baby with neural tube defects. Folate plays an important role in the methylation process of the cytoskeleton, as part of the post-translational modifications. These post translational modifications are vital in giving functionality to the proteins.
Doctors usually prescribe folic acid supplements, upto 400 micrograms per day, to women in their first trimester to avoid these defects. Folic acid deficiency-associated NTD account for nearly 70% of the cases worldwide.
Uncontrolled Diabetes
If the mother has uncontrolled gestational diabetes, there are high chances for the baby to have NTD. Maternal diabetes particularly affects the gene set responsible for neural tube defects.
Weight Gain
Obesity in the expecting mother is found to be a risk factor for the occurrence of neural tube defects.
Medications During Pregnancy
Certain medicines, particularly those that are taken to control seizures, have an adverse effect of the organ formation and development of the foetus. Anti-epileptic drugs like carbamazepine and Valproate show increased risk of causing neural tube defects.
Smoking
Primary or secondary exposure to smoking increases the chances of the mother delivering a baby with NTD. The chemicals in the cigarette are likely to hamper the folate-mediated methylation process
What Is Spina Bifida?
Spina bifida is what is known as a neural tube defect. It occurs during development prior to birth. It’s when the spinal cord, brain, or meninges (their protective covering) does not completely develop. It can be anywhere along the spine and usually can be seen in an opening in the baby’s back at birth. It may also appear as a sack of fluid that has grown outside the body on the spine. This sack may or may not include the spinal cord inside.
Types of Spina Bifida
There are two forms of Spina Bifida: spina bifida occulta and spina bifida cystica.
1. Spina Bifida Occulta
Occulta is a Latin word which means ‘hidden’. In this condition, the affected area may be covered by a layer of skin, a patch of hair, etc. It has no major complications with most parents not even knowing that their child has a medical condition. This is a mild type of spina bifida. It does not cause any disabilities and may go unnoticed until later in life. There is usually no opening in the baby’s back, but only a gap in the spine. In this type, there is no damage to the spinal cord or the nerves.
2. Spina Bifida Cystica
Spina bifida cystica is characterized by the presence of a sac or a cyst, as a large blister at the back of the baby which is covered with a thin layer of skin.
Spina bifida cystica is of two types:
Myelomeningocele
A large fluid-filled sac bulges out of the baby’s back as meninges and in the spinal cord. At times, the sac bursts during childbirth exposing the spine and nerve. This is the most common and serious type of spina bifida. It involves a sack outside the opening in the baby’s back somewhere on the spine. This sack contains parts of the spinal cord and nerves. The spinal cord and nerves in the sack will be damaged.
People with myelomeningocele have physical disabilities that range from moderate to severe. These disabilities may include:
· incontinence
· difficulty going to the bathroom
· inability to move or feel their legs or feet
Meningocele
This is the rarest form of spina bifida and less serious than myelomeningocele. Babies born with this condition have a fluid-filled sac on the head, neck or back. The sac can be as large as a grapefruit or as small as a grape. Babies with this condition can have a problem controlling bowel movements and can suffer from paralysis.
Symptoms of spina bifida
The symptoms of spina bifida are different for each type. They can also vary from person to person within each type.
Myelomeningocele
Symptoms of myelomeningocele spina bifida include:
· open spinal canal over some vertebrae, usually in the middle or lower part of the back
· membranes and spinal cord pushed outside the back in an exposed or skin-covered sack
· weak or paralyzed leg muscles
· seizures
· deformed feet
· hips that are not even
· scoliosis (curved spine)
· issues with the bowel and bladder
Meningocele
Symptoms of meningocele type of spina bifida include:
· small opening in the back
· sack that’s visible at birth
· membranes pushing out through the opening in the vertebrae into sack
· normal development of the spinal cord
Membranes can be surgically removed in cases of meningocele.
Spina bifida occulta
Symptoms of spina bifida occulta include:
· a gap in between vertebrae
· no visible opening outside
· no fluid-filled sack outside the body
· small birthmark or dimple on the back
· small group or cluster of hair on the back
· an area of extra fat on the back
A person may not ever know they have this type of spina bifida.
Spina bifida in children vs. in adults
Spina bifida is not curable, so it will need to be managed your entire life.
In children
For children, treatment focuses on determining the extent of symptoms and disabilities as they develop and preventing those that can be prevented. Proper rehabilitation and medical interventions will be determined and used throughout the child’s development. Childhood is also the time for parents and medical staff to instill a positive attitude toward treatment and management to help the child develop a positive outlook.
In adults
By adulthood, the majority of symptoms and disabilities are known. Coping mechanisms, medications, therapies, and any walking aids are normally in place. Many children with spina bifida grow up to attend college and have careers. Some also live independently.
However, ongoing medical issues can develop throughout the life of a person with spina bifida. Further, some people with more severe disabilities may struggle socially due to stigma and have difficulty finding careers that will fit with their disabilities. However, a good support network can help ease the negative effects.
Treatment
The treatment for spina bifida will be different for each person because symptoms and severity can vary. In some cases, especially in spina bifida occulta, there may not be any treatment needed.
However, myelomeningocele and meningocele require surgery to put the exposed sack and nerves back in place. Some of it may also require removal. The surgeon will then close the opening over the vertebrae. There may be a shunt put in place to avoid complications later in life. This surgery may be performed shortly after the child’s birth. In some cases, prenatal surgery may be done while the baby is still in the womb. You should talk to your doctor about the benefits and risks of both types of surgery.
Even after surgery is performed, some symptoms and disability can remain. They will need to be managed based on the severity of each symptom. Paralysis and bowel and bladder issues typically remain throughout life. Treatment for remaining symptoms can include:
· additional surgeries
· medications
· physical therapy
· rehabilitation services
· walking aids
Prevention
Spina bifida occurs very early in pregnancy. Most women don’t even know they’re pregnant by the time it occurs. So if you’re trying to become pregnant, you should start taking preventive measures against spina bifida. Follow these preventive steps:
· Take a folic acid supplement as prescribed by your doctor.
· Include leafy green vegetables, nuts, beans, and other foods that contain folic acid in your diet.
· Discuss any medications or supplements you take with your doctor.
· If you have diabetes, make sure it’s under control prior to pregnancy.
· If you’re overweight, you should talk to your doctor about a healthy diet and exercise plan.
· Keep your body from overheating from saunas, hot tubs, or a fever.
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What Is Anencephaly?
Anencephaly is a birth defect in which the brain and bones of the skull don’t form completely while the baby is in the womb. As a result, the baby’s brain, particularly the cerebral cortex, develops minimally. The cerebral cortex is the part of the brain primarily responsible for thinking, movement, and senses, including touch, vision, and hearing.
Anencephaly is considered a neural tube defect. The neural tube is a narrow shaft that normally closes during fetal development and forms the brain and spinal cord. This usually happens by the fourth week of pregnancy, but if it doesn’t, the result can be anencephaly.
This incurable condition affects about three pregnancies per 10,000 in the United States each year, according to the Centers for Disease Control (CDC). In about 75 percent of cases, the baby is stillborn. Other babies born with anencephaly may only survive a few hours or days.
In many cases, a pregnancy involving a neural tube defect ends in miscarriage.
What causes it and who’s at risk?
The cause of anencephaly is generally unknown, which can be frustrating. For some babies, the cause may be related to gene or chromosome changes. In most cases, the baby’s parents have no family history of anencephaly.
A mother’s exposure to certain environmental toxins, medications, or even foods or beverages may play a role. However, researchers don’t know enough about these potential risk factors yet to provide any guidelines or warnings.
Exposure to high temperatures, whether from a sauna or hot tub or from a high fever, may raise the risk of neural tube defects.
The Cleveland Clinic suggests certain prescription drugs, including some of those used to treat diabetes, may increase the risk for anencephaly. Diabetes and obesity may be risk factors for pregnancy complications, so it’s always ideal to talk with your doctor about any chronic conditions and how they may affect your pregnancy.
One important risk factor related to anencephaly is inadequate intake of folic acid. A lack of this key nutrient may raise your risk of having a baby with other neural tube defects in addition to anencephaly, such as spina bifida. Pregnant women can minimize this risk with folic acid supplements or diet changes.
If you’ve had an infant with anencephaly, your chance of having a second baby with the same condition or a different neural tube defect increases by 4 to 10 percent. Two previous pregnancies affected by anencephaly increase the recurrence rate to about 10 to 13 percent.
How is it diagnosed?
Doctors can diagnose anencephaly during pregnancy or immediately after the baby is born. At birth, the abnormalities of the skull can be easily seen. In some cases, part of the scalp is missing, along with the skull.
Prenatal tests for anencephaly include:
· Blood test. High levels of the liver protein alpha-fetoprotein can indicate anencephaly.
· Amniocentesis. Fluid withdrawn from the amniotic sac surrounding the fetus can be studied to search for several markers of abnormal development. High levels of alpha-fetoprotein and acetylcholinesterase are associated with neural tube defects.
· Ultrasound. High-frequency sound waves can help create images (sonograms) of the developing fetus on a computer screen. A sonogram may show the physical signs of anencephaly.
· Fetal MRI scan. A magnetic field and radio waves produce images of the fetus. A fetal MRI scan provides more detailed pictures than an ultrasound.
The Cleveland Clinic suggests prenatal testing for anencephaly between the 14th and 18th weeks of pregnancy. The fetal MRI scan take place any time.
What are the symptoms?
The most noticeable signs of anencephaly are the missing parts of the skull, which are usually the bones in the back of the head. Some bones on the sides or front of the skull may also be missing or poorly formed. The brain also isn’t formed properly. Without a healthy cerebral cortex, a person can’t survive
Other signs may include a folding of the ears, a cleft palate, and poor reflexes. Some infants born with anencephaly also have heart defects.
How is it treated?
There is no treatment or cure for anencephaly. An infant born with the condition should be kept warm and comfortable. If any parts of the scalp are missing, exposed parts of the brain should be covered.
The life expectancy of an infant born with anencephaly is no more than a few days, more likely a few hours.
Anencephaly vs. microcephaly
Anencephaly is one of several conditions known as cephalic disorders. They’re all related to problems with the development of the nervous system.
One disorder similar to anencephaly in some ways is microcephaly. A baby born with this condition has a smaller-than-normal head circumference.
Unlike anencephaly, which is apparent at birth, microcephaly may or may not be present at birth. It can develop within the first few years of life.
A child with microcephaly may experience normal maturing of the face and other parts of the body, while the head remains small. Someone with microcephaly may be developmentally delayed and face a shorter lifespan than someone without a cephalic condition.
Links for reference & further studies,
https://www.healthline.com
https://www.ncbi.nlm.nih.gov
https://pubmed.ncbi.nlm.nih.gov
