Third Trimester Tests

Types of Pregnancy Tests

Pregnancy: Who'd have thought it would require more tests than all your academic years combined? But if you're like most pregnant women, the only tests you'll need in your third trimester are the routine screenings conducted at every prenatal visit: a urine test, blood pressure check, measurement of your uterus, and a check of your baby's heartbeat.

You'll also be tested for group B streptococcus, a bacterium that you can pass to your child during delivery. If you carry the bacterium (up to 30 percent of women do), you'll receive antibiotics during labor to prevent your baby from becoming ill. Your doctor may also give you a pelvic exam to see if your cervix has begun to change in preparation for delivery.

So what other tests can you expect in your final trimester? Fortunately, most pregnant women need few. Your doctor may, however, run some additional procedures if you suffer from a chronic health condition such as diabetes or high blood pressure, or if you're carrying multiples, are past your due date, or your baby appears to be growing too slowly. These conditions can sometimes affect a baby's health and well-being.

Here is a roundup of some tests that are performed late in pregnancy and how they can help you and your baby.

Kick Count

Who gets it: Some women who have chronic health conditions, are carrying multiples, or experience post-term pregnancy may be asked to do a kick-count test routinely. Your healthcare provider may also recommend this test if you don't feel your baby moving.

What it is: Your doctor will ask you to lie on your side and record how long it takes for your baby to move 10 times. On average, it can take anywhere from 10 minutes to two hours.

What the results mean: Ten kicks in under two hours is a sign of a healthy baby. If the number of kicks is below 10 or continues to decrease each time you take the test, your physician may suggest some additional procedures such as a nonstress test. The best time for a kick count is right after you eat because that's when the baby is likely to be most active.

Nonstress Test

Who gets it: Women who are carrying multiples or who have chronic health conditions such as high blood pressure or diabetes. If you have a chronic condition, you may be tested once or twice a week, beginning at 32 to 34 weeks' gestation; if your condition is not under control, your doctor may recommend a nonstress test as early as 26 to 28 weeks.

What it is: An electronic monitor is strapped across your abdomen to record your baby's heart rate as he moves around. Nonstress tests usually take 20 to 40 minutes.

What the results mean: If your baby's heart rate doesn't increase as he moves, he may not be receiving enough oxygen or may be having other problems. However, an abnormal test result does not automatically mean that your baby is in trouble; he could be sleeping. Some doctors might attempt to wake the baby by placing a device on your belly that makes a buzzing sound. If your test results continue to be abnormal, your physician will probably recommend additional testing.

Ultrasound

Who gets it: Ultrasounds are commonly used in pregnancy to determine a baby's due date and fetal development. Most women get one at some point during pregnancy, but if you have a chronic health problem, are carrying multiples, or experience vaginal bleeding (which can be a sign of placental problems), you may require several. Ultrasounds are also used to detect birth defects and to check fetal growth and position.

What it is: Ultrasound tests use sound waves undetectable to the human ear to help produce pictures of your unborn baby in the womb. A small, handheld device that emits sound waves will be rubbed across your abdomen. These waves bounce off the baby and reflect back to the ultrasound machine, creating an on-screen picture. Ultrasounds usually last about 15 to 20 minutes, although a detailed examination (generally done when birth defects are suspected) can take up to several hours.

If your baby seems to be growing too slowly, your doctor may also recommend a new ultrasound test called Doppler velocimetry. This procedure measures blood flow in the umbilical cord and other major fetal arteries to see if the baby is getting enough oxygen. Doctors use this test along with others to see if it's best to deliver the baby early.

What the results mean: When they are administered late in pregnancy, ultrasound examinations can help a doctor evaluate fetal size and growth and check for placental abnormalities.

Biophysical Profile

Who gets it: Women with chronic health problems or overdue babies. It also may be recommended if you have pregnancy complications such as decreased amniotic fluid, decreased fetal movement, or placental irregularities.

What it is: The biophysical profile combines the nonstress test with ultrasound. The ultrasound component measures four fetal characteristics: breathing movements, muscle tone, body movements, and the amount of amniotic fluid. The test may be repeated once or twice a week and takes about 30 minutes.

What the results mean: If your baby does not move within a certain amount of time or your amniotic fluid level is low, the baby might be having problems and could benefit from early delivery. However, your physician may want to perform other procedures before taking action.

In some cases, where a woman is considered high risk, a doctor may monitor a pregnancy with a modified biophysical profile, which combines the nonstress test with just one ultrasound measure -- the amount of amniotic fluid. If your results are abnormal, your doctor will probably suggest a complete biophysical profile or further testing.

Amniocentesis

Who gets it: This test is most commonly done in the second trimester to diagnose or rule out fetal birth defects, and is generally recommended to women who are age 35 or older. Your doctor may also recommend amniocentesis in the third trimester if you are at risk of delivering prematurely or if she believes that your baby has anemia or you have chorioamnionitis, a uterine bacterial infection that can lead to preterm labor. Your healthcare provider may suspect chorioamnionitis if you experience high fevers or uterine tenderness. Fetal anemia commonly occurs in women who are Rh-negative, so your doctor may perform amniocentesis if you test positive for this condition.

What it is: Amniocentesis involves inserting a thin, hollow needle into the uterus and removing a small sample of the amniotic fluid, which contains cells shed by the fetus. These cells can provide your physician with valuable health information about your baby.

What the results mean: If you are at risk of delivering prematurely, amniocentesis can determine whether or not your baby's lungs are mature. Infants born with immature lungs may develop respiratory distress syndrome (RDS), a serious condition in which a newborn's lungs can't inflate properly, compromising his ability to breathe. If the test shows that your child's lungs are immature, your physician will probably treat you with corticosteriods -- drugs to help speed lung development in your baby. Corticosteriods can also work to cut the incidence of RDS by 50 percent, reducing the risk of infant death by one third. Your healthcare provider may also attempt to postpone delivery.

If your doctor recommends some of these tests, try not to worry. Most likely, the results will show that everything is fine. Late pregnancy tests enable you to get the special care you'll need to deliver a healthy baby.

Dr. Schwarz, obstetrical consultant to the March of Dimes, is past president of the American College of Obstetricians and Gynecologists; vice chairman for clinical services, Department of Obstetrics and Gynecology, Maimonides Medical Center; emeritus distinguished service professor of obstetrics and gynecology, SUNY Downstate Medical Center, both in Brooklyn, New York; and fellow of the Royal College of Obstetricians and Gynecologists of Great Britain.

Originally published in American Baby magazine, July 2004.

All content here, including advice from doctors and other health professionals, should be considered as opinion only. Always seek the direct advice of your own doctor in connection with any questions or issues you may have regarding your own health or the health of others.