Pregnant? Your Genetic Testing Options

If you’re pregnant or thinking of getting pregnant, genetic testing can give you a closer look into your health and your baby’s health.

Some tests can check babies for medical conditions while they are in the womb. Others check their DNA for some genetic diseases. Even before pregnancy, genetic carrier screenings can look at the mother’s and father’s genes to show the chances that their child would have a genetic disorder.

Most of the tests are optional, but they can help you make health decisions and know what to expect when your baby comes.

Learn more about each kind of genetic test so you can decide which -- if any -- are right for you.

Before Pregnancy: Genetic Carrier Screening Tests

If you have a gene for a disorder but don’t have the condition yourself, you’re called a carrier. Genetic carrier screening tells you if you and your partner have these genes and, if so, the chances you’ll pass them on to your children.

You can get the tests either before or during pregnancy, but they’re most useful beforehand.

A doctor will take a sample of your blood or saliva for testing. The lab can look for genes for many types of disorders, but the more common ones are:

People from some ethnic groups may be more likely to be carriers for some conditions, so ask your doctor if you’re in a high-risk category. Common groups that may want carrier testing include non-Hispanic whites (cystic fibrosis), people of Eastern European Jewish descent (Tay-Sachs disease, cystic fibrosis, and others), and those of African, Mediterranean, and Southeast Asian backgrounds (sickle cell disease).

First Trimester Screening Tests

Once you get pregnant, your doctor might suggest checking your baby’s genes for the risk of a medical problem. Typical tests in the first stage of pregnancy are:

Sequential screen: This test uses a mix of ultrasound and blood tests to look for the risk of Down syndrome, trisomy 18, and spine and brain problems. You get it between 10 and 13 weeks of pregnancy. If the results are negative, you can choose to have more testing in your second trimester.

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Integrated screening: Another mix of ultrasound and blood tests to look for the risk of Down syndrome, trisomy 18, and spine and brain problems. You get it around 12 weeks, and a second part of it happens during your second trimester. It’s slightly more accurate than a sequential screen, but it takes longer to get the results -- until after the second part of the test.

Cell-free fetal DNA testing: Some of your baby’s DNA winds up in your blood. After 10 weeks, your doctor takes a sample from you, and a lab tests the baby’s DNA in it for signs of:

  • Down syndrome
  • Trisomy 18
  • Trisomy 13
  • Problems with sex chromosomes

If any of your screening tests shows a risk of a birth defect, your doctor will suggest a diagnostic test to confirm the results. The cell-free DNA test does not look for problems with the brain or spine, so if you get it, you can also get another blood test in your second trimester to detect those problems.

Second Trimester Screening Tests

In this part of your pregnancy, there are a few typical tests your doctor will offer:

Maternal serum quad screen: This blood test looks for proteins in your blood that can mean your baby has a higher risk of Down syndrome, trisomy 18, and spine or brain problems. Your doctor can do the test between 15 and 21 weeks.

Integrated screening (part two): If you got the first part of this test in your first trimester, you’ll have another blood test between 16 and 18 weeks.

Ultrasound: Around week 20, a technician uses a machine to make images of your baby using sound waves. Your doctor uses these pictures to look for birth defects like cleft palate, heart problems, and kidney problems.

Diagnostic Tests: Amniocentesis and Chorionic Villus Sampling (CVS)

Amniocentesis and CVS check babies before they are born for possible birth defects, such as:

  • Down syndrome
  • Trisomy 13
  • Trisomy 18
  • Problems with brain or spine growth, like spina bifida (Only amniocentesis can spot these.)

They can also find some genetic disorders. Both tests are over 99% accurate.

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Most women don’t get these tests. They have a very small risk of causing a miscarriage, and most people who get screening tests that don’t show any problems feel comfortable relying on those results alone. But the screening tests are not 100% accurate. So if your screening results show that your baby might have a birth defect, or if you want the most accurate tests, your doctor may suggest CVS or amniocentesis.

CVS tests a small part of your placenta in your uterus. Your doctor gets this tissue either with a needle through your stomach or with a thin tube into your cervix. Doctors do CVS early in pregnancy, between your 10th and 13th week. The test may cause cramps, bleeding, or infection for some women.

During amniocentesis, your doctor puts a long, thin needle through your belly and into the sac that surrounds your baby to take out a small amount of fluid. A lab studies the proteins and cells in the fluid. The test is safest between 15 and 20 weeks. Sometimes, amniocentesis may can cause bleeding, cramping, or infection.

If your doctor suggests one of these tests for you, it doesn’t mean there’s definitely a problem with your baby. It means she wants to make sure everything is OK or follow up on the results from another screening test you had.Talk with her about the pros and cons of these tests, as well as what the results might mean for you.

WebMD Medical Reference Reviewed by Traci C. Johnson, MD on June 02, 2018

Sources

SOURCES:

American Academy of Family Physicians: “Prenatal Diagnosis: Amniocentesis and CVS.”

National Women’s Health Resource Center: “What to Expect from Prenatal Genetic Testing.”

Johns Hopkins Medical Health Library: “Amniocentesis,” “Genetic Carrier Screening.”

University of California San Francisco Medical Center: “FAQ: Chorionic Villus Sampling (CVS).”

Cleveland Clinic: “Genetic Amniocentesis.”

Emory University School of Medicine: “About Amniocentesis.”

Northwestern University: “Genetic Screening and Testing During Pregnancy.”

National Human Genome Research Institute: “A Brief Primer on Genetic Testing.”

The American College of Obstetricians and Gynecologists: “Preconception Carrier Screening,” “Cell-free DNA Screening for Fetal Aneuploidy.”

Mayo Clinic: “Down Syndrome.”

Society for Maternal-Fetal Medicine: “Cell free DNA screening is not a simple blood test.”

Eunice Kennedy Shriver National Institute of Child Health and Human Development: “What tests might I need during pregnancy?”

Cincinnati Children’s Hospital Medical Center: “Whole Exome Sequencing.”

Levenson, D. American Journal of Medical Genetics, published online January 2016.

© 2018 WebMD, LLC. All rights reserved.

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