A Guide to Late Pregnancy Tests

Here is a summary of third trimester prenatal tests:

Third Trimester

*Biophysical Profile (BPP)-This noninvasive test combines ultrasound with a nonstress test to evaluate your baby's health during the final trimester of pregnancy. The BPP is indicated when the baby's health is in question or the pregnancy is deemed high risk.

The nonstress test (NST) involves strapping 2 belts to the mother's tummy to measure the baby's heart rate and the mother's contractions for a period of 20-30 minutes to evaluate the baby's breathing, moving, muscle tone, heart rate, and amniotic fluid levels.

The ultrasound test is performed for up to an hour. Some experts caution against lengthy ultrasounds.

Total Score

The total score of these two tests tell your doctor if your baby needs to be delivered early. The BPP is performed after 32 weeks of gestation.

*Fetal Non-Stress Test (NST)-The Fetal Non-Stress test is a noninvasive test performed after 28 weeks gestation. Two belts are strapped across the mother's abdomen and the baby's heart rate is monitored for up to half an hour. NST is performed when the baby seems sluggish, is overdue, the placenta is suspected of malfunctioning, or the pregnancy is high risk. NST can help evaluate your baby's oxygen intake and can predict fetal distress.

*Glucose Challenge Screening & Glucose Tolerance Test (GCT, GTT)-Some pregnant women develop the condition known as gestational diabetes which poses a risk to mother and infant. The first test, GCT, is the early screening test and is performed between weeks 26 and 28 of the pregnancy. If there is a positive result, the second test, the GTT, may be indicated. The GTT diagnoses diabetes by showing how your body utilizes a type of sugar called glucose.

Liquid Glucose

GCT is a part of standard prenatal testing, and the GTT is done only when a GCT suggests a need for further testing. In the GCT, the mother is given liquid glucose to drink and her blood is drawn an hour later. A positive test indicates high levels of blood glucose and a need to perform a GTT.

Carbohydrates must be included in your diet during the three days before a GTT is performed. You will need to fast 14 hours before the test is performed so schedule a GTT for early morning. Get someone to drive you to the test facility and back since you may feel weak. Your blood will be drawn to establish your baseline fasting blood glucose level, and then you will drink glucose solution. Your blood will be drawn and tested 3 times over the next three hours. Abnormal results indicate a need for dietary changes and retesting at a later date. If two readings are abnormal, the diagnosis of gestational diabetes is confirmed and you will need a treatment plan.

Bacterial Infection

*Group B Strep Infection-Group B streptococcus (GBS) is a bacterial infection that can affect the vagina or rectum of a pregnant woman. The bacteria can be passed on to a baby during delivery in 1 out of every 2,000 babies. GBS is rare in pregnant women and the mother doesn't always pass on the bacteria to her newborn, but when the baby is affected, there can be serious consequences to his health.

The GBS is therefore a part of routine testing and performed during weeks 35 and 37 of the pregnancy. Swabs are taken from the vagina and rectum and analyzed. Results are available within 48 hours. If the results are positive, your doctor will treat you with antibiotics during your labor.