Your Guide to Prenatal Testing

When you’re pregnant, prenatal tests give you information about your health and your baby’s. They help detect any problems that could affect him, like birth defects or genetic diseases. The results can help you make the best health care decisions before and after your child is born.

Prenatal tests are helpful, but it’s important to know how to interpret what they find. A positive test result doesn’t always mean your baby will be born with a disorder. You’ll want to talk with your doctor, midwife, or other health care provider about what the tests mean and what you should do once you have the results.

Doctors recommend some prenatal tests for all pregnant women. Only some women will need other screening tests to check for certain genetic problems.

Routine Prenatal Tests

There are different prenatal tests you can get in your first, second, and third trimester. Some check your health, and others get information about your baby.

Throughout your pregnancy, you’ll get routine exams to make sure you’re healthy. Your health care provider will check samples of your blood and urine for certain conditions, including:

She’ll also check your blood type and whether your blood cells have a protein called the Rh factor. You may also get:

  • Pap smear
  • Group B Strep screening. Your doctor will swab the skin in and around your vagina to check for this type of bacteria. This usually happens in the last month before you give birth.
  • Ultrasound. This technology uses sound waves to make pictures of your baby and your organs. If your pregnancy is normal, you’ll have it twice, once near the beginning to see how far along you are, and the second time around 18-20 weeks to check your baby’s growth and make sure his organs are developing properly.

Prenatal Genetic Tests

Doctors also can use prenatal tests to look for signs that your baby is at risk for certain genetic disorders or birth defects. You don’t have to have these tests, but your doctor may suggest some to make sure your baby is healthy.

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They’re especially important for women who have a higher risk of having a baby with a birth defect or a genetic problem.This is you if you:

Some prenatal genetic tests are screening tests. They tell you if your baby has a higher risk of having a certain disorder or disease, but they can’t tell you for certain that he’ll be born with it. Other “diagnostic” tests will give you a more definite answer. Usually, you’ll get this kind after you have a positive result on a screening test.

To start, your doctor may want to test you and the child’s other parent for the genes that cause certain genetic diseases, like cystic fibrosis, Tay-Sachs disease, sickle cell disease, and others. If both of you have a gene for one of these diseases in your DNA, you could pass it on to your baby, even if you don't have the disease itself. The exam is called a carrier test.

Your doctor can use one or more different screening tests to check your baby for a genetic problem, including:

Ultrasound. You’ll already have one of these early in your pregnancy to make sure everything is going well. But if you have a high-risk pregnancy, you’ll need this exam more often. Around 11-14 weeks, doctors can use it to look at the back of your baby’s neck. Folds or thick skin there could mean a higher risk of Down syndrome. Your doctor also may take a sample of your blood at the same time.

Integrated Screening. There are two phases to this test. In the first part, doctors combine the results of the ultrasound looking at your baby’s neck and the blood tests you got at 11-14 weeks. Then, they’ll take a second blood sample between 16-18 weeks. The results measure your baby’s risk for Down syndrome and spina bifida, a spinal cord and brain disorder.

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Sequential Screen. This is similar to integrated screening, but your doctor reviews the results with you right after the first phase at 11-14 weeks. It’s not as accurate as the longer test, but it lets you know your baby’s risk earlier. If the screening finds there may be a problem, your doctor will use more tests to find out for sure. If it doesn’t find a risk, you’ll most likely get the second blood test at 16-18 weeks to be safe.

Triple or quadruple screening test. Doctors check your blood for hormones and proteins that come from your baby or your placenta, the organ that brings him oxygen and nutrients. The test can look for three different substances (triple screening) or four (quadruple screening). Certain amounts of these mean your baby has a higher chance of having a birth defect or a genetic disease. This test happens in the second trimester, usually at 15 to 20 weeks.

Cell-free fetal DNA testing. Doctors use this test to find your baby’s DNA in your blood and check it for Down syndrome and two other genetic conditions, trisomy 18 and trisomy 13. You can have this done after 10 weeks of your pregnancy. Doctors don’t recommend it for every woman, usually only those who have a high-risk pregnancy. It’s not available everywhere, and some health insurance policies don’t cover it. Talk to your doctor about whether you need this test.

Other Tests

If you get a positive result on a screening, your doctor can use other tests to look for a problem.

Amniocentesis. Using a thin needle in your belly, your doctor will take a sample of the fluid that surrounds your baby and check it for genetic disorders or birth defects. The procedure does carry some risk. About 1 in 300 to 500 women will miscarry because of amniocentesis. Your doctor can tell you if it’s important for you to have this.

Chorionic villus sampling (CVS). Doctors take a small piece of your placenta by putting a needle through your belly or a small tube up your vagina. They test the sample for Down syndrome and other genetic conditions. Only some high-risk women will need this test, usually if a screening found a risk of a birth defect. The procedure will tell you for sure if there’s a problem, but it also comes with a risk of miscarriage that’s similar to amniocentesis. Talk to your doctor about whether you should have CVS.

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What Do I Do Once I Have the Results?

Prenatal test results can help you make important health care decisions. But it’s important to remember that many of them tell you it’s possible, but not certain, that your baby will be born with a disorder. No test is 100% accurate.

Talk to your doctor about the results you get and what they mean. A genetics counselor can also help you decide what to do after a positive result and what life will be like for your child if he has a disorder.

Questions for Your Doctor

If your doctor recommends prenatal testing, consider asking:

  • Why do I need these tests?
  • What will the results tell me? What will they not show?
  • What happens if I don't get the test?
  • What will I do with the results?
  • How accurate are the tests?
  • What are the risks?
  • How long will it take to get the results?
  • What does it feel like?
  • How much do they cost?
  • Will my insurance cover them?
  • Will anyone else (like my insurance company) have access to the results, especially of genetic tests?
  • What will the results mean for my family?
  • Can I decide not to get the results even if the test has already been done?
  • Where do I get the tests done?
WebMD Medical Reference Reviewed by Traci C. Johnson, MD, FACOG on September 24, 2014

Sources

SOURCES:

March of Dimes: "Prenatal Care."

Neil Seligman, MD, University of Rochester Medical Center.

Kids Health from Nemours: "FAQs: Prenatal Tests."

American College of Obstetricians and Gynecologists: "Frequently Asked Questions- Routine Tests in Pregnancy."

Cleveland Clinic: "Maternal-Fetal Medicine (High-Risk Pregnancy).

Johns Hopkins Medicine: "Common Tests During Pregnancy."

Ryan E. Longman, MD, University of Miami, Miller School of Medicine.

Eunice Kennedy Shriver National Institute of Child Health and Human Development: "How do health care providers diagnose birth defects?"

Cystic Fibrosis Foundation: "About CF: What Is Cystic Fibrosis?"

Eunice Kennedy Shriver National Institute of Child Health and Human Development: "The Placenta: A Vital Organ for Baby, Mom and Science."

University of California San Francisco Medical Center: “FAQ: Cell-Free Fetal DNA Testing.”

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