Prenatal tests

What are prenatal tests and why are they important?

Prenatal tests are medical tests you get during pregnancy. They help your health care provider find out how you and your baby are doing.

You get some prenatal tests several times during pregnancy at your prenatal care checkups. These tests make sure you and your baby are staying healthy. There are other tests that are done at certain times during your pregnancy. These prenatal tests check to see if your baby has any health problems, including:

• Birth defects. These are health conditions that are present at birth. They change the shape or function of one or more parts of the body. Birth defects can cause problems in overall health, how the body develops or how the body works.
• Genetic and chromosomal conditions. These conditions are caused by changes in genes and chromosomes. A gene is part of your body's cells that stores instructions for the way your body grows and works. A chromosome is the structure in cells that holds genes. Genetic conditions include cystic fibrosis (also called CF), sickle cell disease and heart defects. A common chromosomal condition is Down syndrome. Sometimes these conditions are passed from parent to child, and sometimes they happen on their own.

If there is a history of certain health conditions in your family, you may want to talk with a genetic counselor. A genetic counselor has training to help you understand about birth defects and other medical conditions that run in families and how they can affect your health and your baby's health.

What are screening tests and diagnostic tests?

Screening tests check to see if your baby is more likely to have a health condition, but they don’t tell you for sure if you baby has a condition. There are no risks to you or your baby when you have a screening test.

Diagnostic tests tell you for sure if your baby has a health condition. If a screening test shows your baby is at high risk of a health condition, your provider may recommend a diagnostic test to confirm the results. Some diagnostic tests may have some risks for your baby, like miscarriage. Miscarriage is when a baby dies in the womb before 20 weeks of pregnancy.

Screening test results can help you decide if you want to have a diagnostic test. You may or may not want to know if your baby has a health condition. If you decide to have a diagnostic test, you can learn more about your baby’s condition and how to care for your baby after he’s born. You also can make plans to give birth in a hospital that can give your baby special medical care.

What prenatal tests do you get all through pregnancy?

You can get these prenatal tests several times during pregnancy:

• Blood pressure check. Your provider checks your blood pressure to make sure you don’t have preeclampsia. Preeclampsia is high blood pressure that can happen after the 20^th week of pregnancy. Preeclampsia can cause serious problems during pregnancy.
• Urine test. Your provider checks your urine for infections, like a bladder or kidney infection, and other conditions, like preeclampsia. Having protein in your urine may be a sign of preeclampsia.
• Blood tests. Your provider checks your blood for certain infections, like syphilis, hepatitis B and HIV. Your blood test is also used to find out your blood type and Rh factor and to check for anemia. Anemia is when you don't have enough healthy red blood cells to carry oxygen to the rest of your body. Rh factor is a protein that most people have on their red blood cells. If you don’t have it and your baby does, it can cause Rh disease in your baby. Treatment during pregnancy can prevent Rh disease. 

Your provider also checks your weight at each prenatal care checkup to make sure you’re gaining the right amount.

What prenatal tests are done in the first trimester?

You may have several tests in your first trimester (months 1, 2 and 3). Talk to your provider to find out which tests are right for you.

• Carrier screening for genetic conditions. This screening test checks your blood or saliva to see whether  you’re a carrier of certain genetic conditions that could affect your baby. If you’re a carrier, it means you don’t have the condition yourself but you do have a genetic change that you can pass to your baby. If both you and your partner are carriers of the same condition, there is a greater risk that your baby will have the condition. Carrier screening can be done before pregnancy or during the early weeks of pregnancy. If results show that you or your partner is a carrier, you may be able to find out if your baby has the condition or is a carrier of the condition. Talk to your health care provider about what carrier screening tests might be right for you.
• Cell-free fetal DNA testing (also called noninvasive prenatal screening or testing). This screening test checks your blood for your baby’s DNA. The DNA is examined for certain genetic conditions, such as Down syndrome. This test is done after 9 weeks of pregnancy. Your provider may recommend the test if an ultrasound shows your baby may have a birth defect or if you've already had a baby with a birth defect. If you have this test, your provider may recommend you have a diagnostic test, like amniocentesis, to confirm the results. 
• Chorionic villus sampling (also called CVS). This diagnostic test checks tissue from the placenta to see if your baby has a genetic condition. CVS is done at 10 to 13 weeks of pregnancy. Your provider may want you to have CVS if you’re older than 35, if there’s a history of genetic conditions in your family or if your first-trimester screening shows that your baby is at increased risk for birth defects.
• Early ultrasound (also called first-trimester ultrasound). Ultrasound uses sound waves and a computer screen to make a picture of your baby inside the womb. Your provider may use early ultrasound to make sure that you’re pregnant or to date your pregnancy so you know how far along in pregnancy (how many weeks) you are.
• First-trimester screening. This screening test includes a blood test and an ultrasound to see if your baby may be at risk for some birth defects, like Down syndrome and heart defects. The test usually is done at 11 to 13 weeks of pregnancy.

What tests are done in the second trimester?

Your provider may offer you these prenatal tests in your second trimester (months 4, 5 and 6 of pregnancy):

• Maternal blood screening (also called quad screen). This screening test checks your blood to see if your baby may be at risk for some birth defects, such as Down syndrome. It’s called a quad screen because it measures 4 substances in your blood: alpha-fetoprotein (AFP), estriol, human chorionic gonadostropin (hCG) and inhibin A. The test is done at 15 and 22 weeks of pregnancy.
• Ultrasound. Your health care provider will perform an ultrasound between 18 and 22 weeks of pregnancy. The ultrasound will check your baby’s growth and development and check for any birth defects.
• Amniocentesis. During amniocentesis, a sample of  amniotic fluid is taken from around the baby. The fluid is tested to see if your baby has a birth defect or genetic condition. The test usually is done at 15 to 20 weeks of pregnancy. Your provider may want you to have amniocentesis if you’re older than 35, if there is a history of genetic conditions in your family, or if your first-trimester screening shows that your baby is at increased risk for birth defects. 
• Glucose screening. This screening test checks to see if you may have gestational diabetes. This is a kind of diabetes that some women get during pregnancy. You get this test at 24 to 28 weeks of pregnancy.

What tests are done during the third trimester?

In your last trimester (months 7, 8 and 9 of pregnancy), your provider does a test for group B strep (also called GBS). Group B strep is an infection you can pass to your baby during birth. The test checks fluid from your cervix to see if you have GBS. You get this test at 35 to 37 weeks of pregnancy.

What are kick counts and how do you do them?

Kick counts (also called fetal movement counts) is a way for you to track how often your baby moves. By about 5 months (20 weeks) of pregnancy, you should start to feel your baby move in your belly. Your baby can turn from side to side and sometimes head over heels. Tell your provider if:

• You’re at about 20 weeks of pregnancy and haven’t felt your baby move.
• You’re worried that your baby isn’t moving.
• You notice a change in how often your baby moves, especially if movement decreases.

Your provider may ask you to do kick counts to see when and how often your baby moves. Here are 2 ways to do kick counts:

1. Every day, time how long it takes for your baby to move 10 times. If it takes longer than 2 hours, tell your provider.
2. See how many movements you feel in 1 hour. Do this 3 times each week. If the number changes, tell your provider. 

You can do kick counts even into your third trimester. If your provider is concerned about your baby’s movements, they may do other tests to check on your baby’s health.  

More information

• Einstein Victor Center for the Prevention of Jewish Genetic Diseases
• Genetic Alliance 
• JScreen at Emory University
• National Organization for Rare Disorders (NORD)
• National Society of Genetic Counselors

Last reviewed: September, 2020