Contraction Stress Test

Oxytocin Challenge Test

Test Overview

A contraction stress test checks to see if your unborn baby (fetus) will stay healthy during the reduced oxygen levels that normally occur during contractions when you are in labor. The test includes external fetal heart monitoring (nonstress test). The test is done when you are 34 or more weeks pregnant.

During a uterine contraction, the blood and oxygen supply to your baby drops for a short time. This is not a problem for most babies. But the heart rate of some babies gets slower. This change in heart rate can be seen on the external fetal monitoring device.

For a contraction stress test, the hormone oxytocin is given to you in a vein (intravenously, or IV) to cause labor contractions. You may also massage your nipples. This tells your body to release oxytocin. If your baby's heart rate slows down (decelerates) in a certain pattern instead of speeding up (accelerating) after a contraction, your baby may have problems with the stress of normal labor.

A contraction stress test is usually done if you have an abnormal biophysical profile. A biophysical profile uses ultrasound during a nonstress test to measure a series of physical characteristics of your baby. During the test, uterine contractions, fetal breathing, fetal muscle tone, fetal movements, and amniotic fluid volume are measured. A contraction stress test gives a better picture of your baby's health than the nonstress test. You may have more than one contraction stress test during your pregnancy.

Some doctors may do a biophysical profile or a Doppler ultrasound test instead of a contraction stress test.

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Author:	Maria G. Essig, MS, ELS	Last Updated: February 22, 2008
Medical Review:	Kathleen Romito, MD - Family Medicine Liisa Honey, MD, FRCSC - Obstetrics and Gynecology
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