The prenatal tests you may receive and what they mean
It goes with the territory: When you’re pregnant, you can’t help but worry about the health of your baby. Fortunately, there are a host of prenatal tests that can help ease your fears and make even a healthy pregnancy less stressful. Following is a rundown of the tests you’re most likely to undergo; see the chart at right for detailed information.
During pregnancy, women undergo several screening tests to rule out preexisting health problems and potential problems with the fetus. Most women’s prenatal testing begins with the first visit to the obstetrician or midwife, at which blood and urine tests will be done, as well as a Pap smear, if necessary. Several tests will be performed at later visits to track your pregnancy and monitor your baby’s health. For example, at each visit, your blood pressure will be measured and a sample of your urine examined. The doctor will note your weight and may listen to the baby’s heartbeat and take external measurements of your uterus to monitor the baby’s growth. At some point, an ultrasound may be performed to determine your due date or check your baby’s development.
One of the newer tests is cystic fibrosis screening, which determines whether a woman or her partner is a carrier of the disease. While the test is available to all pregnant women, your doctor or midwife will probably recommend it if you are of European or Ashkenazi Jewish descent. If you are interested in having the test done, ask your doctor. It is usually done via a blood sample in early pregnancy.
Other screening tests include the maternal serum alpha-fetoprotein (MSAFP or AFP), which is performed at about 15 to 20 weeks. This blood test helps screen for such conditions as neural-tube defects and Down syndrome. The results of the AFP test are not conclusive, however; abnormal results simply indicate that more testing is necessary.
If any of your screening tests produces abnormal results, if you have a personal or family history of birth defects or if you will be over the age of 35 when you deliver, you may undergo certain diagnostic tests to rule out problems with the fetus. The two most common are amniocentesis and chorionic villus sampling (CVS).
Amniocentesis can detect all known chromosomal “errors,” such as Down syndrome, as well as many genetic disorders. It is typically performed between the 15th and 20th week of pregnancy; a needle is inserted through the abdomen into the uterus to withdraw a sample of amniotic fluid. Because it is an invasive test, there is a 1 in 200–400 risk of miscarriage following the procedure.
CVS, which also can detect chromosomal or genetic birth defects, has a slightly higher risk of miscarriage (1 in 100–200), but it can be performed as soon as 10 weeks after conception. With this procedure, a needle is inserted through the abdomen or a catheter is inserted through the vagina to take a sample of the outer fetal membrane. If amniocentesis or CVS testing is indicated, you may want to consult a genetic counselor or your religious adviser to discuss the kinds of decisions such testing may lead to. For more information about prenatal testing, contact the March of Dimes at 888-663-4637, www.marchofdimes.com; or the American College of Obstetricians and Gynecologists at 202-863-2518, www.acog.org.