Third Trimester Tests During Pregnancy

Medically Reviewed by Traci C. Johnson, MD on March 22, 2023
3 min read

These tests are common in the third trimester of pregnancy:

Blood and urine tests: Your doctor will continue to check your urine for protein and sugar and any signs of infection, keeping a close eye for signs of preeclampsia, a complication that is most common in the last weeks of pregnancy. You may have blood tests again for anemia.

Other measurements: Weight, blood pressure, and fundal height measurements (distance from your pubic bone to the top of your uterus) also continue. Your baby's heartbeats are loud and clear!

Pelvic exams: In the last few weeks of pregnancy, your doctor will start doing pelvic exams again. This is to see if the cervix has started the ripening process for birth. Ripening is the softening, thinning, and opening (dilating) of the cervix.

These changes can happen slowly or quickly during the weeks, days, or hours before birth. So it's not uncommon to dilate a few centimeters a few weeks before your due date and then to stop dilating. This process is somewhat unpredictable.

Group B streptococcus screening: Vaginal and rectal swabs are taken at 35 to 37 weeks of pregnancy to detect group B strep bacteria. Although group B strep can be present in up to 30% of all healthy women, it's the leading cause of life-threatening infections in newborns and can also cause intellectual disability, impaired vision, and hearing loss. Women who test positive are treated with antibiotics during delivery to protect the baby from contracting the infection at birth. As an alternative, your physician or midwife may choose not to test for strep but to treat you in labor if certain risk factors develop.

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

Nonstress test: Done weekly in many high-risk pregnancies, such as in cases where a women is carrying more than one fetus, or has diabetes or high blood pressure, this test involves using a fetal monitor strapped across the mother's abdomen to measure the baby's heart rate as it moves. It's also used for monitoring overdue babies.

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

Ultrasound: Most pregnant women have just one or perhaps two ultrasounds. If you're having twins, you'll have this test more often, perhaps right up until birth, to check the position and growth of your babies. When needed, doctors can combine nonstress tests with ultrasound. This allows your doctor to check the babies' breathing motions, body movements, and muscle tone as well as the amount of amniotic fluid.

Biophysical profile: Can be done with just an ultrasound or with a combination of a nonstress test and an ultrasound.