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The Basics about Prenatal Tests
Mary’s late-in-life pregnancy at 45 thrust her into a world filled with unknowns. Unfortunately, her first ob-gyn, who specialized in high-risk pregnancies, made a scary situation worse.
“During my second visit, the nurse called me an ‘elderly mother’—despite the fact that I was in excellent shape. Then she told me that because of my age, my baby would test positive for every abnormality,” Mary recalled. She cried for hours after hearing the “what could be wrong with the baby” list. Midway through her pregnancy, Mary felt pressured by her ob-gyn to take a genetic screening blood test that he told her would reveal all her baby’s abnormalities.
Like Mary, you will be offered different tests during your pregnancy. It’s helpful to have a basic understanding of common prenatal tests—and their risks and benefits—before you are in the emotionally and hormonally charged throes of a late-in-life pregnancy.
Common Prenatal Tests
First Trimester:
ULTRASOUND: An ultrasound machine uses sound waves that reflect off the baby to create a computer-generated image. Often a first trimester ultrasound is more accurate in determining gestational age—how old the baby is—than using the dates of a woman’s last menstrual period.
CHORIONIC VILLUS SAMPLING: Performed between 10 and 12 weeks, CVS is a first-trimester invasive test that involves sampling tissues between the placenta and the uterus. A thin plastic tube is inserted through the cervix and guided to the placenta, where the cells are extracted. The advantage of CVS over amniocentesis is that the results are available earlier in the pregnancy. CVS has a 1 to 1.5 percent miscarriage rate.
Second Trimester
ULTRASOUND: A second semester ultrasound is an excellent tool to examine the baby’s anatomy. Abnormalities such as heart or brain defects can often be identified at this stage of the pregnancy.
AMNIOCENTESIS: Performed between 15 and 20 weeks, this is an invasive screening test. The procedure involves inserting a needle through the mother’s abdomen into the uterus to collect a sample of amniotic fluid surrounding the baby. It has a miscarriage rate of 0.5 percent and a 1 to 2 percent rate of complications such as vaginal bleeding or leaking amniotic fluid. Earlier amniocentesis can be performed at 11 to 13 weeks, but it has a higher rate of miscarriage.
QUAD SCREEN: This is a maternal fetal blood test usually done between 15 and 20 weeks—although the best time to obtain the test is between 16 and 18 weeks. The quad screen test is for four things:
- Maternal serum alpha-fetoprotein—proteins made by the baby found in the mother’s blood. Levels either too high or too low can be suggestive or neural tube defects or twins or triplets.
- Human chorionic gonadotropin (HCG)—hormone produced by a woman’s placenta during pregnancy
- Estriol—hormone produced by the mother
- Inhibin A—a clygoprotein. Levels are elevated in a woman carrying a baby with Down syndrome
The value of all four tests from a single blood specimen is used to more accurately predict risk of neural tube defects, such as spina bifida, or chromosomal abnormalities. Blood values vary depending on the age of the fetus. Therefore, accurate gestational age is important to ensure that the risk prediction is valid. If a quad screen returns abnormal, an ultrasound may be performed to ensure accurate gestational age.
Realize that prenatal tests may change from year-to-year. At your first ob-gyn visit, ask your health-care provider what tests are recommended. Legally, a physician must inform you of the different genetic tests. However, you cannot be forced to take any test. Decide what tests you will or won’t have, based on your personal beliefs and desires.
~Adapted from Baby Changes Everything: Embracing and Preparing for Motherhood after 35 by Beth K. Vogt