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Common Prenatal Tests

During your monthly checkups, your caregiver will weigh you, check your blood pressure, and take a urine sample to test for sugar or protein in your urine (which can signal gestational diabetes or pregnancy-induced high blood pressure). Finally, she'll measure your abdomen to see if your baby is growing at the expected rate.

Your caregiver may also offer you a battery of prenatal tests now, including:

  • Maternal multiple marker screening - These tests - AFP, triple screen, or quad screen - measure levels of biochemical markers in your blood to try to predict your fetus' risk of various genetic problems and birth defects between 15 and 20 weeks. Alpha-fetoprotein (AFP) is a substance produced by the fetus. Elevated AFP is associated with problems in the fetal spinal cord, such as spina bifida, and a number of other birth defects. The triple screen measures AFP, estriol, and hCG. The newer quad screen adds another hormone called inhibin A. Abnormal levels of these substances can indicate an increased risk for problems such as neural tube defects or Down syndrome. The tests do not diagnose these conditions, however. If your screening test is abnormal, your caregiver will suggest additional tests, such as ultrasound and amniocentesis, to help determine why. One in 20 women having a serum test will have an abnormal result, but far fewer women will have a baby with a problem.
  • Ultrasound - Using high-frequency sound waves, ultrasound creates a "picture" of your developing baby. It helps your caregiver pinpoint the fetus' age, detect multiple fetuses, and spot conditions such as neural tube defects.
  • Amniocentesis - This procedure can detect or rule out disorders such as Down syndrome and neural tube defects. Guided by ultrasound, a doctor or medical technician inserts a needle through your abdomen and into the amniotic sac. She then draws out a small sample of amniotic fluid. The sample is sent to a lab, where fetal cells are grown and analyzed for chromosomal defects. This test is generally offered only to women who have an increased risk for having a baby with genetic defects -- women over 35 with abnormal serum screening results, or those with a family history of inherited disorders.
  • Glucose tolerance testing - This test checks for signs of gestational diabetes. It's fairly straightforward: You drink a sweetened solution, and an hour later a blood sample is drawn and your blood sugar level is measured.
  • Hemoglobin testing - This test measures the amount of red blood cells in your blood. Too few can indicate anemia, a common (and easily remedied) problem during pregnancy.

Common 1st Trimester Prenatal Tests

In the first trimester, you will probably receive a group of tests known in many health centers as the "prenatal panel." This panel of tests usually includes, but is not limited to, a complete blood count (CBC), blood typing (including Rh screen), rubella viral antigen screen, hepatitis panel, and urine analysis. Other tests may be obtained based on your health and previous pregnancy history.

An ultrasound may be obtained in the first trimester to determine the health of the pregnancy. The ultrasound also will confirm the due date, and that the fetus is inside the uterus and is not an ectopic pregnancy. Most diagnostic ultrasound exams occur in the second trimester.

Advances in prenatal diagnosis now allow for detection of possible genetic problems during the first trimester. Using ultrasound, doctors can measure the back of the fetus’ neck (called the nuchal translucency) to assess the risk of Down syndrome. When combined with a serum test for biochemical markers, this first trimester test is better than other screening test for picking up Down syndrome. The test results may be used alone or in combination with the multiple marker screen to determine the risk of Down syndrome.

A test called chorionic villus sampling (CVS) can detect Down syndrome and other genetic disorders as early as 10 weeks into a pregnancy. It is as accurate as a second trimester amniocentesis, but carries additional risks. To determine which procedure is right for you, discuss the various options with your health care provider, a genetics counselor, or a maternal-fetal specialist.

Common 2nd Trimester Prenatal Tests

The second trimester is an important time for the main screening tests to determine how you and your baby are doing. The first ultrasound (also called a sonogram) is typically done early in the second trimester, to check on your baby's health and age. If needed, a second ultrasound examination is usually done at the end of the second or the beginning of the third trimester. This one confirms the findings from the first ultrasound, and checks to see how the baby is developing. Ultrasound and maternal serum screening (see above) together can help assess your risk of having a baby with problems.

Late in the second trimester, you are screened for diabetes, hepatitis B, retested for sexually transmitted infections, and may have a pelvic examination to detect whether your cervix is weak or dilating.

Common 3rd Trimester Prenatal Tests

A few weeks before your due date, your health care provider will perform the test that checks for group B strep infection on the perineum. About 20% of all women may be carriers of this bacteria. It usually does not cause any illness for adults, except occasional urinary tract infections. We now know that group B strep is the number one cause of newborn infection in those who develop sepsis (systemic infection). Women who test positive for group B strep will receive intravenous antibiotics in labor.

In the third trimester, it is still common for your health care provider to perform cervical exams if you have signs of labor or if ruptured membranes are suspected. If it appears that the baby is not as active as expected, or if you have any high risk factors, your baby may be watched more closely. A non-stress test, which tracks the baby’s heart rate and contractions over a 20 minute period, is a common test used in the third trimester. Ultrasounds are also used to assess the baby's growth, check how well the baby is moving, and detect abnormalities if they are suspected.

Review Date: 12/9/2012
Reviewed By: Irina Burd, MD, PhD, Maternal Fetal Medicine, Johns Hopkins University, Baltimore, MD. Review provided by VeriMed Healthcare Network.
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