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10 Facts about Prenatal Genetic Testing


Prenatal genetic testing can be very confusing and emotional. With help from Jennifer Hoskovec, the Director of the Prenatal Genetic Counseling Services at the University of Texas Medical School at Houston, here are some answers to some of the hardest questions parents are asking.

1. Carrier Screening Can Be Done Before Pregnancy

a woman talking to a female doctor

Carrier screening is a standard blood test that can be done on a woman prior to getting pregnant or during a pregnancy that tests for recessive conditions and diseases. There are different "panels" a.k.a. batches of carrier screening available, sometimes depending on ethnic background. If a woman tests positive in a carrier screening, the same test is offered to the father. If the father also tests positive, there is a 25 percent likelihood that the fetus will have that condition. To discuss subsequent tests and expanded carrier screening, contact your doctor or a genetic counselor.

2. First and Second Trimester Tests Are Standard Practices

a woman receiving an ultrasound from a doctor

A nuchal translucency test is offered in the first trimester of a pregnancy. Through blood work and an ultrasound, this test is used assess risks for Down Syndrome as well as other more severe and less common chromosome abnormalities. If a nuchal translucency test is not done in the first trimester, a "quad screen" blood test is offered in the second trimester. These standard tests do not pose risks to a pregnancy. To understand more about these tests, contact your doctor or a genetic counselor.

3. Amniocentesis Samples Amniotic Fluid

an illustration of genetic testing

Amniocentesis is typically offered between the 16th and 24th weeks for women at increased risk for chromosome abnormalities or other genetic conditions due to family history, maternal age or an abnormal nuchal translucency or quad screen. Amniocentesis is performed by putting a needle into the mother’s abdomen to get a sample of the amniotic fluid around the baby. Using this sample, doctors are able to get more accurate information. This is a diagnostic test and poses a 1/3% chance or less complication with the pregnancy. Complications could include bleeding, fluid or a miscarriage. Amniocentesis may not be offered in some regions so you should talk to your doctor or genetic counselor for further information.

4. Chronic Villus Sampling (CVS) Tests Placenta Tissue

an illustration of a human embryo

CVS happens between the 11th and 13th weeks--earlier than an amnio, which some women prefer. CVS is also an invasive test, but rather than sampling amniotic fluid, it samples the placenta's tissue. Reasons to get a CVS include having a previous pregnancy with an abnormality, a family history that includes genetic conditions, an abnormal first trimester screening result, or being a mother over 35 years old. CVS poses a slight risk to the pregnancy of 1% or less, depending on the practitioner. Complications might involve bleeding, fluid loss, or miscarriage. CVS is only available in certain regions. Talk with your doctor or genetic counselor to find out more information about CVS.

5. Non-Invasive Prenatal Testing (NIPT) is the Newest Test

an illustration of a DNA chain

NIPT is a new (as of fall 2011) blood test that women can have beginning at nine weeks of pregnancy. NIPT, also known as cell-free DNA screening, measures fetal DNA in the mother’s bloodstream and can identify specific chromosome abnormalities such as trisomy 13 and trisomy 18. The benefits of NIPT are that it is non-invasive and has shown a higher accuracy rate than the first and second trimester screens. There are no risks with NIPT but there are limitations. It is a screening test, not a diagnostic test like amniocentesis or CVS, and a positive result could require women to undergo further testing. To get more information about NIPT, contact your doctor or genetic counselor.

6. Oral Glucose Tolerance Tests Are Standard

two doctors are standing over a woman sitting on a chair

An Oral Glucose Tolerance Test is for gestational diabetes that women develop during the course of the pregnancy. Gestational diabetes only occurs in women who do not have diabetes prior to pregnancy. The test is given between the 24th and 28th weeks of pregnancy and involves drinking a glucose liquid followed by a blood test 60 minutes later. If blood sugar is too high, the doctor will give you a longer, second test; it's possible to "fail" the first screening and then be totally fine on the second. If gestational diabetes goes untreated, it can pose risks to the fetus such as growing too large, problems with the birth, or additional issues after delivery. This test is offered to all pregnant women.

7. Anatomy Scans (Ultrasounds) Measure the Baby—and Count Fingers and Toes

a pregnant woman receiving a scan

At 20 weeks, your doctor will likely offer an anatomy scan. This ultrasound gives the care-provider an opportunity to see the baby and check its measurements as well as look for any abnormalities in the body, including the intricate areas of the heart. Depending on your doctor, ultrasounds may be offered monthly after the 20th week or only toward the end of the pregnancy. Speak with your doctor about the frequency of scans available to you. Most studies show these scans as safe, but some emerging science says it's wise to limit unnecessary scans; do your research.

8. Who Is At Risk Is Always Evolving

a close up of the dictionary definition of genealogy

The highest risk situations are those with a family history with a genetic condition, those who have had a previous pregnancy with an issue, or have had miscarriages. These criteria are starting to exceed the importance of the mother being over 35 years old. Doctors are moving away from ethnic-based carrier screening as ethnicity is getting harder to define. Sickle cell anemia is still more common in African Americans. Tay-Sachs, familial dysautonomia, Canavan disease, and cystic fibrosis are more common to Ashkenazi Jews with Eastern European backgrounds. As information evolves, you should talk to your doctor or genetic counselor.

9. Genetic Tests Aren’t Required

a closeup of a test tube with a pink liquid in it

Parents are offered genetic tests but they must decide how much information they want about the baby and how it would be used. Parents often choose genetic testing to prepare themselves for complications during the pregnancy or post-pregnancy. Doctors and genetic counselors are critical to aiding parents by providing resources, referrals, and balanced information. It is important to determine where your doctor is in the evolution of these tests. If your doctor does not have a genetic counselor to refer you to, you can go to the National Society of Genetic Counselors website and type in your zip code.

10. Insurance Doesn’t Always Cover Genetic Testing

a closeup of a stethoscope and pen

Insurance coverage for genetic testing is highly dependent on the kinds of tests you're getting and your insurance carrier. Routine genetic tests, such as the carrier screening, the nuchal translucency and the quad tests are usually covered to some extent. Newer tests, such the NIPT, may not be covered. Many doctors’ offices may be familiar with the guidelines for each insurance policy but families may want to investigate for themselves whether they have a policy on genetic screening.

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