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Beginnings: Pregnancy, Birth & Beyond

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Third trimester: Screens and tests

After 28 weeks you will probably see your health care provider every other week until 36 weeks. After that you are likely to have weekly visits.

 

Screen or test Why it may be given

Biophysical profile

This test is the combination of an ultrasound and nonstress test (see below). The ultrasound provides information about the amount of amniotic fluid. It can also provide information about your baby's muscle tone, activity, and breathing movements.

It assesses your baby's well-being in the last weeks of pregnancy. If a pregnancy is high-risk or over 40 weeks, it helps determine whether to start labor.

Contraction stress test or oxytocin challenge test

You are given a medicine (usually Pitocin®) to start contractions. An electronic fetal monitor tracks and records these contractions and your baby's heart rate.

This test shows whether your baby is getting enough oxygen to handle contractions well. It helps determine whether to start labor or deliver the baby by Cesarean. It may be done if a nonstress test indicates there might be a problem.

Fetal fibronectin test

A swab is used to get a sample of the discharge from your vagina. This is checked for fibronectin, a glue-like substance that connects the amniotic sac around your baby to the inner wall of your uterus.

If you are having contractions between weeks 23 and 34, the presence of fibronectin means you are at risk for preterm birth.

Group B streptococcus

Your vagina and anus are swabbed. The secretions are cultured to see if the bacteria are present.

Group B streptococcus is on the skin of 10 to 30 percent of American women. It does not cause illness in adults but can cause a very serious illness in newborns. If the bacteria are present, you will be given intravenous (IV) antibiotics in labor. This will help prevent your baby from getting sick. The test is done between 35 and 37 weeks.

Hemoglobin

Your blood is drawn and tested for the number of red blood cells.

This is a test for anemia. If the hemoglobin in your red blood cell count is low, you may need to take iron supplements and eat more iron-rich foods.

Non-stress test

An electronic fetal monitor records your baby's heart rate for 20 to 30 minutes. During that time you indicate when you feel your baby move. Sometimes sound or vibration is used to get your baby to move.

This test gives information about your baby's health. Normal changes in the heart rate when your baby moves indicate well-being. This test can be combined with an ultrasound as part of a biophysical profile.

Rh antibody test:

A small amount of your blood is drawn and tested for antibodies.

This test is done to see if you have produced antibodies that can hurt your baby's blood. This test is only done if you are Rh negative.


 

Source: Allina Health's Patient Education Department, Beginnings: Pregnancy, Birth and Beyond, sixth edition, preg-ahc-90026, ISBN 1-931876-25-8

First published: 10/04/2002
Last updated: 08/22/2011

Reviewed by: Allina Health's Patient Education Department experts