Prenatal Genetic Testing: What You Need to Know for Your Pregnancy
Genetic testing is a standard part of pregnancy, but it isn't a requirement, or even always helpful. Here's what expecting parents need to know.
Genetic testing is now a commonplace part of pregnancy. Testing for inherited diseases is a standard practice, ordered by doctors as part of the routine prenatal checklist, and is usually covered by health insurance. Autosomal recessive inherited disorders, another name for passed down genetic illnesses, are something that doctors use prenatal genetic testing to detect, so that expectant parents can decide if the information changes their willingness (or ability) to bring their baby into the world.
Prenatal genetic testing can also give parents and doctors a heads up. Having the information in advance that a baby has a 25 percent chance of developing Cystic fibrosis, allows doctors to test for it as part of the baby’s newborn screening. With Cystic fibrosis, early identification and treatment are key to controlling many of the symptoms, enabling children to live longer, healthier lives. Essentially, genetic testing during pregnancy gives you more information about medical decisions you may have to make in the future.
Prenatal Genetic Screening Tests
“Testing” is essentially a global term for all the various ways your partner can be poked, prodded or scanned. The two subcategories to testing are screening and diagnostic tests. Screening tests are usually the first to be done. They will use the mother’s blood serum and a specialized ultrasound to determine the risks of certain genetic issues. While it’s technically correct to call chromosomal screening a genetic test, since all genetic material is contained in chromosomes, Dr. Ira Jaffe, OB/GYN at Rosh Maternal & Fetal Medicine in New York City recommends sticking to the term chromosomal, to avoid confusion. Chromosomal testing is the standard blood test that expectant mothers do at 10 weeks to check for the presence of extra chromosomes, and therefore the potential risk of conditions including Down syndrome. Based on the results, or if the mother is 35 or older, expecting parents may opt for additional tests done on the fetus itself. They come with a tremendous caveat: the results of screening can only tell if there is an increased risk. It does not mean your child is necessarily afflicted by a genetic disorder even with higher risk indications.
Blood Tests: Using the mother’s blood (thank goodness, right?), this screening looks for a variety of protein and hormonal markers that are associated with an increased risk of anencephaly, spina bifida and Down syndrome. It’s performed in the first trimester.
Nuchal Translucency: This sounds like something more likely associated with a deep-sea jellyfish. But the nuchal translucency screening is a specialized ultrasound that measures the thickness of your kids neck, which determines if they could be affected by issues like Down syndrome (or just getting hella jacked with in-utero free weights). These are also performed in the first trimester by someone who is specialized in the procedure.
Prenatal Genetic Diagnostic Tests
When it is determined that there is an increased risk for genetic issues, diagnostic testing will be recommended. These tests come second because they are invasive and rely on amniotic fluid and placental samples. Because of that they also carry a small risk of complications that include miscarriage.
Amniocentesis: Brace yourself for this one. Through the abdomen and into the womb, a fine needle is inserted. Then, a tiny amount of amniotic fluid containing live fetal cells is extracted Live fetal cells from a tiny amount of amniotic fluid. If you aren’t squeamish about needles (you freak) then go ahead and be there for this one.
This test is the most accurate way to determine a large number of genetic abnormalities. And as a consolation prize, is also the most accurate way to determine the kid’s sex. Because it is invasive, it does carry with it some small risks to both the mother and the baby. It can be done up to the third trimester of pregnancy in some instances.
Chorionic Villus Sampling (CVS): Try not to confuse this one with where you get your prophylactics and Steel Reserve. This test samples tissue from the placenta via a small tube inserted through the cervix. It can be done as early as week 10. Unlike amniocentesis, CVS doesn’t detect neural tube defects. It also comes with a slightly more elevated risk for complications.
What to Do with the Genetic Test Answers
Expectant parents put a lot of emphasis on chromosomal and genetic test results, and rightfully so. But Dr. Jaffe says the most critical conversation may be the one that happens before the genetic tests are administered. “You should think of a medical test, any medical test, whether it’s a maternal blood test or a biopsy, as you’re asking a question,” he says. “It’s a question. Don’t assume that you’re going to get the answer you want.” He stresses the importance of thinking about the potential answers beforehand and having a candid conversation with your partner. That way, the question, as well as its answer, becomes more actionable, and ultimately less stressful.
Most facilities also provide genetic counseling to help parents interpret their test results, both the mathematics of probability (like the fact there’s a 1 in 4 chance that a baby whose parents are carriers of Cystic fibrosis will be affected by the disease) and beyond. “What parents do in those situations is a very personal choice” says Jaffe. “We arm them with the information they need.”
Is Testing Always Required?
Screening and diagnostic testing are not compulsory and there are plenty of reasons a couple may not want to go down the prenatal genetic testing road. One of the biggies is that these tests can sometimes result in false positives that could lead to further unnecessary testing and add a ton of undue stress.
There’s also the anxiety factor. Some feel that knowing their child has a genetic disorder would not change how they would approach the remainder of the pregnancy. Therefore they may opt-out of testing to avoid that kind of anxiety.
However, your doctor will encourage prenatal tests in a few specific instances:
- There is a disorder that runs in your family (aside from being annoying at Thanksgiving).
- You and your partners both carry a recessive gene linked to a birth defect.
- You have a previous child with a chromosomal disorder.
- The mother is over the age of 35, which is considered an advanced age for pregnancy and makes you feel like you’re in Logan’s Run.
You can keep calm by going in informed, despite the fact that tests are universally reviled and stress inducing. And at least with prenatal genetic testing, there aren’t any Scantrons. So no need for a perfectly sharpened number 2 pencil. Bonus!
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