Third Trimester Prenatal Tests

As you enter the third trimester, your care team may recommend additional tests based on your health history, age and other risk factors. These tests help your OB ensure you and your baby are healthy and ready for delivery.

Your provider — and sometimes a genetic counselor — will review which tests are right for you and answer any questions you have.  

Common Prenatal Tests in the Third Trimester 

Biophysical Profile (BPP) 
A combination of ultrasound and fetal monitoring that checks your baby’s heartbeat, movements, breathing pattern, placenta and the amount of amniotic fluid. Think of it as a thorough “in utero” checkup.  

Contraction Stress Test (CST) 
Assesses how your baby handles the stress of contractions. Uterus contractions are brought on by gently stimulating your nipples, and your baby’s heart rate is monitored.

Nonstress Test (NST) 
Checks your baby’s well-being by monitoring their heart rate during movement using an electronic fetal monitor. 

Oxytocin Challenge Test (OCT) 
Similar to the CST, but contractions are started with a small dose of oxytocin (pitocin) through an IV. This is usually done if nipple stimulation doesn’t bring on strong enough contractions. 

Group B Streptococcus (GBS) 
GBS is a common bacteria that can be passed to your baby during birth. Around 35–37 weeks, your provider will take a quick swab of your vagina and rectum to test for it. If GBS is present, you’ll receive antibiotics during labor to protect your baby from infection.