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Third Trimester Prenatal Tests

A rundown of the prenatal tests you may get during your third trimester—and what they're testing for.

All those pee cups and needlesticks starting to blur together? This guide to the most common third trimester tests should help you keep things straight. You’ll definitely receive these screenings, and those marked optional should be discussed with your doctor.

[ ] Urine Tests
At every appointment, you’ll give a urine sample to be screened for glucose (elevated levels can be a sign of gestational diabetes) and protein (a possible indication of preeclampsia or a urinary tract infection). If either shows up in your urine, your doctor will likely order order additional testing.

[ ] Glucose Tolerance Test (optional)
Between weeks 24 and 28, almost all women are screened for gestational diabetes mellitus (GDM). If you have specific risks, you might take it earlier. The test can’t diagnose GDM, but will determine whether further testing is necessary.

[ ] Group B Strep Test
This test, given to all women around week 36, screens for harmless bacteria in the rectum and vagina that can be dangerous if transmitted to baby during delivery.

[ ] Nonstress Test (optional)
If you’re overdue or at risk of premature labor, or if there are signs of fetal distress, your doctor may perform a nonstress test to measure fetal heart rate and movement and uterine activity. This test can be done anytime after 24 to 26 weeks, but is most commonly performed late in the third trimester.

[ ] Biophysical Profile (optional)
Usually performed with the nonstress test in the third trimester, a biophysical profile shows baby’s heart rate, activity level, breathing movements, muscle tone and the amount of amniotic fluid in the uterus. Your doctor might recommend it if you’re carrying multiples, are past your due date, or have risk factors such as high blood pressure or kidney or heart disease.