There’s a lot to think about during pregnancy. And we’ll be honest: Some of those thoughts can be a little scary. If you feel your pulse quicken at mention of prenatal screening tests, you’re not alone — but knowledge is power.
Let’s demystify the testing you’ll receive (or perhaps opt out of in some cases) during your pregnancy. And remember, your doctor is an important ally — if you have any concerns about specific tests or results, they’re on hand to answer your questions.
“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.
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.
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.
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.
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!
A quad marker screening test is a blood test conducted during the second trimester. It can help your doctor learn if you’re increased risk of carrying a baby with Down syndrome, neural tube defects, and abdominal wall abnormalities. It measures four of the fetal proteins (thus, “quad”).
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.
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.
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
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:
- lower intestinal tract
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.
Prenatal screening tests can be an important source of information for pregnant people. While many of these tests are routine, some can be a much more personal decision.
Talk to your doctor about your concerns if you’re not sure if you should be screened or if you’re feeling anxious. You can also ask to be referred to a genetic counselor.
Your healthcare team can discuss the risks and benefits with you and help you decide which prenatal screenings are right for you.