Third-Trimester Examinations and Tests

Third-Trimester Examinations and Tests


At each prenatal visit in the third trimester, you'll be weighed, and your blood pressure and urine will be checked. Your doctor or midwife will measure the size of your uterus (fundal height) and feel your belly. This is done to check your baby's growth and position.

Late in the third trimester, your doctor or midwife will check to see how far your baby's head has dropped into your pelvis. If your baby is not head-down after 36 weeks, you may have a fetal ultrasound to confirm the position. Your care provider may try version to gently turn the baby into a head-down position.

Close to delivery, you may be checked to see if your cervix has begun to thin (efface) and open.

Third-trimester tests

Late in pregnancy, you may be checked for:

Group B strep.

A woman who has group B strep in her vagina can pass it to her baby during vaginal birth. This can cause severe problems for the baby. If you test positive for group B strep (or you are not tested), you will be treated with antibiotics during labour.

Hepatitis B.

If you test positive for hepatitis B, your baby will be treated within 12 hours after birth.

In the third trimester, your care provider may recommend an amniocentesis if:

  • You are going to deliver early. This test can show if your baby's lungs are developed enough for delivery.
  • There is a concern about infection in the amniotic fluid.

Depression screening

Your care provider may check with you about your mood. It's important to find and treat depression. This can help prevent problems during pregnancy and after delivery.

If you have your first prenatal visit during your third trimester, you'll have more than these tests. Other tests you may have include tests for blood type, anemia, and HIV. You may be screened for hepatitis B, sexually transmitted infections, or thyroid disease. You'll also be checked for past infections, such as syphilis or rubella (German measles).


Current as of: November 9, 2022

Author: Healthwise Staff
Medical Review:
Sarah Marshall MD - Family Medicine
Kathleen Romito MD - Family Medicine
Adam Husney MD - Family Medicine
Kirtly Jones MD - Obstetrics and Gynecology