Overview

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 (dilate) (Figure 1).

Third-trimester tests

Late in pregnancy, you may be checked for:

Group B strep.

If you have group B strep in your vagina, you can pass it to your 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.

Your healthcare provider will also recommend:

• You have Tdap vaccine (previously called the dTap vaccine). The best time to get it is when you’re between 27 and 32 weeks pregnant. In some situations your healthcare provider may recommend Tdap be given earlier. Talk to your healthcare provider about when to get the Tdap vaccine.
• You have the influenza vaccine during influenza season if you have not already had it earlier in your pregnancy. You can get influenza vaccine anytime during your pregnancy. (Find out more about immunizations and pregnancy.)

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).

Figure 1 - Cervical effacement and dilation

Effacement (thinning)

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As labour nears, the fetus's head drops down into the pelvis and pushes against the cervix. The cervix begins to thin (efface), sometimes over a few weeks.

Dilation (opening)

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At the same time, the cervix also begins to open (dilate).

Current as of: April 30, 2024

Author: Ignite Healthwise, LLC Staff
Clinical Review Board
All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.