Parent Corner: Prenatal testing--beyond finding out boy or girl
By John Eggers, MD, Tim Ransden, MD, and Ann Hoffman, DO
Cascade Valley Arlington Women's Health
It used to be finding out the sex of your new baby was one of life's biggest surprises. Now parents can learn the answer to this question, as well as take a peek into the health of their unborn child. Prenatal testing can provide information about potential genetic problems, chromosomal defects, and physical malformations.
Different kinds of tests
Prenatal tests fall into two categories: screening and diagnostic. Screening tests, such as basic ultrasound and tests of the mother's blood are done even when there are no apparent risk factors. These types of tests can help your doctor find any hidden risk factors that may exist. From there, diagnostic testing can provide enough information to determine if your baby has a medical condition.
Screening Tests
The maternal triple test is the screening test we use at Cascade Valle Arlington Women's Health. This test looks for substances that normally show up in the blood of pregnant women:
- Maternal serum alpha-fetoprotein (MSAFP) - a protein normally produced by a fetus.
- Human chorionic gonadotropin (HCG) - a hormone produced in the placenta.
- Estriol - an estrogen produced by both the fetus and the placenta.
High levels of AFP may indicate the fetus has a neural tube defect, most commonly spina bifida or anencephaly. Low levels of AFP may indicate Down syndrome.
Abnormal levels of HCG and estriol may indicate chromosome abnormalities.
The results of these tests are most accurate if done between 15 and 20 weeks of when the baby is conceived. While it takes several days to get the test results back from the lab, there are no potential risks or side effects.
Diagnostic Testing 1,2,3
The three most common prenatal diagnostic tests are ultrasound, amniocentesis, and chronic villus sampling.
- Ultrasound - High-frequency sound waves are used to create pictures of what's going on inside your body. (95% of the time the ultrasound machine is "listening" to the sound wave energy coming back, only sending out energy 5% of the time.) The images can reveal major structural abnormalities, including congenital heart defects. A basic exam lasts about 20 minutes, but a more detailed one may last much longer.
- Amniocentesis - Samples of amniotic fluid are removed using a needle and then tested for specific genetic disorders (cystic fibrosis), chromosome abnormalities (Down Syndrome), and neural tube defects (spina bifida.) Though typically done after the baby has been growing for 15 weeks, it also may be used shortly before delivery to determine if your baby's lungs have developed enough to breathe on its own. (The amniocentesis tests done later in your pregnancy are less risky than those done earlier.) Results may take two or more weeks. An ultrasound is used to determine the safest site for the needle to enter. This test carries a slight risk of miscarriage, ranging from 1 in 400 to 1 in 200.
- Chorionic Villus Sampling (CVS) - Samples of the cells that line the placenta, known as chorionic villus cells, are removed and tested for genetic abnormalities such as Down syndrome and cystic fibrosis. This test can be done at 10 to 12 weeks and preliminary results are available in two days, final results in about a week. This test carries a slightly higher risk of miscarriage, about 1 in 100.
The choice of whether to test is ultimately up to you, the mother. No one should force you in this decision. Many women choose not to have the tests because the conditions being tested for cannot be changed prior to birth. Other women want to be as prepared as possible and so choose to have the tests performed. Prenatal diagnostic testing is offered to parents with specific risk factors:
- The mother is 35 years of age or older.
- There is a history of birth defects in the family.
- Maternal screening test results are abnormal.
Discussing concerns about the tests with your doctor or genetic counselor before hand may be helpful.
Almost Always a Healthy Baby
Not everything can be tested for.
Not every disease and condition can be diagnosed in the womb. So, unfortunately a normal test result does not always mean problems can't develop. Fortunately, more than 95 percent of pregnancies end with the birth of a healthy baby!
Disclaimer: This information is provided for educational purposes only. It should not replace a visit with your health care professional. Call your doctor if you need more information or have additional questions.