Third Trimester Testing

1 What are Third Trimester Tests During Pregnancy?

Common tests, done during the third trimester of pregnancy are:

Group B streptococcus screening is done by taking vaginal and rectal swabs at 35 to 37 weeks of pregnancy to detect group B strep bacteria because it can cause life-threatening infections in newborns and cause mental retardation, hearing loss and impaired vision. If the test is positive, the woman is treated with antibiotics during delivery to protect the baby from contracting the infection at birth.

Electronic fetal heart monitoring is done during pregnancy after 20 weeks, labor, and delivery to monitor the heart rate of the fetus to indicate whether the fetus is doing well or is in trouble.

Nonstress test (NST) performed after 28 weeks with a belt placed around the mother’s belly so it can measure the baby’s heart rate in response to its own movements. It is done weekly in high-risk pregnancy (women with twins, diabetes or high blood pressure) and for monitoring overdue babies.

Contraction stress test is done in high-risk pregnancies by a fetal monitor which measures the baby's heart rate in response to contractions stimulated either by Oxytocin (Pitocin) or nipple stimulation to predict how well the baby will cope with the stress of labor.

Biophysical profile combines a nonstress test with an ultrasound for a more accurate evaluation of the baby.

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