Genetic Screening During Pregnancy: What You Should Know
Genetic screening during pregnancy can seem overwhelming for parents-to-be. There are so many tests and so many options. But remember that any and all decisions you make are your own. Sometimes it's easy to forget that you have the final say, despite recommendations and statistics. Let's break down some of the tests you'll hear about to give you a better understanding.
More: Should I Take An At-Home Genetics Test During Pregnancy?
Screening Tests
Screening tests are non-invasive and optional. The Department of OBGYN at Northwestern Medicine explains screening tests perfectly:
"The benefits of the screening tests are that they involve no risk to you or the pregnancy for miscarriage and they provide additional information about the chance that your pregnancy has certain birth defects. The limitations of screening tests are that they will not give you a "yes or no" answer about whether or not your baby has a birth defect and they only provide information about a limited number of birth defects. Screening tests are designed to determine a more accurate risk (or chance) for birth defects, not to diagnose them. Most women who have screening tests use them to help decide if they want to proceed with further diagnostic testing."
Think of these tests as a safe first step. There are three common screening tests done throughout your pregnancy.
Sequential Screen This screen identifies the risk of Down Syndrome, Trisomy 18, and neural tube defects like spina bifida. First, you'll have an ultrasound to check the development of the baby's neural tube. Usually a genetic counselor will meet with you after the ultrasound to discuss results and next steps.
At this point it's up to the patient to decide how to proceed. My husband and I took a few minutes alone to decide what we were going to do. Your options are usually to decline blood work to screen for Down Syndrome and Trisomy 18, or proceed. If you proceed with blood work, you would get results in a few weeks, and then determine if further diagnostic testing is needed.
Maternal Screen This screen is taken by drawing blood during weeks 15-21 of your pregnancy. This is another non-invasive measure to screen for Down Syndrome, Trisomy 18 and neural defects. This is commonly done with mothers who didn't have the sequential screen during their first trimester.
18-22 Week Ultrasound During this ultrasound, expecting mothers often discover the sex of their baby, but there is much more to it than that. Your ultrasound tech will look for any potential heart defects, a cleft lip, kidney problems and brain and limb abnormalities. If any indications of a potential problem are found, a genetic counselor will discuss your options in detail.
Diagnostic Tests
Diagnostic tests are invasive and usually done after an initial finding during your screening tests.
CVS (Chorionic Villus Sampling) The CVS test is done early in pregnancy, usually at 10-13 weeks, and it takes a closer look to see if the baby may have Down Syndrome, Trisomy 18 or Trisomy 21. This test examines a small piece of the mother's placenta to determine the risk of chromosomal abnormalities. According to Northwestern Medicine, the associated risk of miscarriage after a CVS is performed is 1/250 to 1/300.
Amniocentesis An amniocentesis can be performed anytime during pregnancy, but is commonly done during weeks 15-18. Again, this test takes a close look at your baby's risk for Down Syndrome, Trisomy 18, 13 and other abnormalities. A sample of amniotic fluid is taken when a needle is inserted into the mother's abdomen. Within the amniotic fluid are also the baby's cells which are then examined via genetic testing. Northwestern Medicine assigns a 1/500 to 1/1,000 risk of miscarrige after an amniocentesis.
Genetic screening during pregnancy is a serious subject. Education and time can help you process all the information and make the best decisions for you and your baby.
