Tests You Need During Pregnancy

Prenatal tests are important for your health and your unborn baby's health. Here's what to expect.

"Taking good care of yourself during pregnancy is the most important way to have a healthy baby," says E. Charles Lampley, MD, assistant professor at the Chicago Medical School and an ob-gyn at Mount Sinai Hospital in Chicago.

There are a number of prenatal tests you'll go through while you're pregnant, but the very first test you'll take is the one that will tell you whether you're actually pregnant in the first place. "To get off to a healthy start, it is important to know that you are going to have a baby as early into the pregnancy as possible," Lampley says. If you have regular periods and you miss one, that's a pretty good sign (although not a foolproof one). Another indication, he says, is simply whether you think you're pregnant. "It's a life-altering event, and the psychological part can clue you in."

If you do think you're pregnant, have your hunch confirmed through a blood test at your doctor's office or a health clinic, Lampley says. You can use a drugstore test first, but he cautions that these are only about 75% accurate. Tests performed at the doctor's office are almost 100% accurate.

Once you know for certain that you're pregnant, schedule regular appointments -- even if you're feeling fine. "Unless there are risk factors, you should see your obstetrician once a month for the first 28 to 32 weeks," Lampley says. "Women who develop diabetes or high blood pressure during pregnancy, or who have a history of delivery before 37 weeks, should see the doctor more often."

According to Boris Petrikovsky, MD, PhD, chairman of the department of obstetrics and gynecology at Nassau University Medical Center in East Meadow, N.Y., and author of What Your Unborn Baby Wants You to Know, your first prenatal visit will include blood tests to determine your blood type; your iron level to see if you're anemic; your blood glucose level to check for diabetes; and your Rh factor (if your blood is Rh negative, and the father's is Rh positive, the fetus may inherit the father's Rh-positive blood, which could cause your body to make antibodies that would hurt your unborn child). You will also be tested for HIV, hepatitis B, and syphilis, as well as whether you're immune to rubella (German measles), since coming down with this illness while pregnant, especially in the first three months, can cause birth defects.

A Pap smear -- if one has not been performed recently -- will be done to test for early cervical cancer and sexually transmitted diseases such as chlamydia and gonorrhea, while a urine specimen will be taken to check for urinary tract infections. A blood pressure check will also screen for high blood pressure, which can interfere with the blood supply to the placenta.

These tests are all routine and are performed on every pregnant woman, Petrikovsky says.

The next set of prenatal tests will be performed between weeks 8-18 of the pregnancy, Petrikovsky says, and will include an ultrasound screening, which can help determine your due date more accurately, and also look for abnormalities in the fetus. During this time, your doctor will also take other blood tests (known as a triple screen or a quad screen) that will measure blood levels of alpha-fetoprotein, estriol, hCG (human chorionic gonadotropin), and inhibin, which can indicate whether the fetus is at risk for abnormalities such as Down syndrome or spina bifida. A newer blood test, PAPPA (pregnancy-associated plasma protein A), conducted during weeks 10-14 of the pregnancy and used in conjunction with an ultrasound screening, is a good choice for women who are at risk of having a baby with a chromosomal abnormality, says Petrikovsky.

Depending on the results of the blood tests, the age of the mother (ages 35 and above), or the family history of the mother-to-be, the doctor may then suggest further prenatal tests, such as chorionic villus sampling (CVS) or amniocentesis, both of which detect Down syndrome or other abnormalities. CVS, which is usually done between weeks 10-12 of the pregnancy, can be performed either by passing a thin tube from the vagina into the cervix to remove a sample of tissue from the chorionic villi (which makes up the placenta), or by inserting a needle through the abdominal wall to obtain a tissue sample. Amniocentesis, which is performed between weeks 16-18 of the pregnancy, involves the insertion of a needle through the abdominal wall into the uterus, removing some of the amniotic fluid. Both CVS and amniocentesis carry a small risk of miscarriage.

Between weeks 24-28, you will be screened again for diabetes (some women develop pregnancy-related diabetes, known as gestational diabetes, which usually clears up after the baby is born), and patients who are Rh negative will be checked for Rh antibodies (which can be treated through a series of injections), says Petrikovsky.

At the end of the pregnancy, between weeks 32-36, you may be retested for syphilis and gonorrhea, as well as for group B strep (GBS), a type of bacterium that can cause meningitis or blood infections in newborn infants; if you test positive for GBS, you will be given antibiotics during labor and delivery to minimize the risk of transmitting the bacterium to your infant.

Though these are all routine tests, there may be other prenatal tests that your obstetrician will recommend, depending on your racial or ethnic background or family medical history, says Vivian Weinblatt, MS, CGC, regional manager of genetic services for Genzyme Genetics in Philadelphia and former president of the National Society of Genetic Counselors.

Certain populations, for example, are at risk for certain diseases, Weinblatt explains. Ashkenazic Jews (those of Eastern European descent) as well as French Canadians and Cajuns are at high risk for Tay-Sachs, a debilitating neurological disease that usually results in a child's early death. Since the increased use of screening tests to determine whether parents-to-be are carriers of Tay-Sachs became more prevalent in the 1970s, the incidence of the disease has dropped dramatically, says Weinblatt.

Weinblatt says other illnesses that are specific to the Jewish population and can be screened with a blood test or tissue sample are Canavan disease; mucolipidosis type 4; Niemann-Pick disease type A; Fanconi anemia type C; Bloom syndrome; familial dysautonomia; and Gaucher disease.

Africans, African Americans, Southern Europeans, and Asians are at higher risk for blood-related illnesses such as sickle cell anemia and thalassemia, says Weinblatt.

If you have a family history of illnesses such as muscular dystrophy, hemophilia, or cystic fibrosis, you may also want to consult a genetic counselor, Weinblatt advises. "A genetic counselor can't treat you or your unborn child, but he or she can let you know how your risk factors can affect your pregnancy.

"When you know ahead of time -- even if you find out that both you and your partner are carriers of a specific illness -- you can prepare yourself emotionally, you can find the proper doctor, etc. You'll have a greater feeling of control when you know what to look for."

However many prenatal tests you have, try not to become too anxious. Remember, says Lampley, that "the vast majority of unborn children are perfectly normal, provided the mother has taken care of herself and her child."