Contraction Stress Test

Oxytocin Challenge Test

Test Overview

A contraction stress test checks to see if your baby (fetus) will be okay with the reduced oxygen levels that normally occur during contractions when you are in labour. The test includes external fetal heart monitoring (non-stress 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. However, some babies get a slower heart rate. 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 labour 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 (accelerates) after a contraction, your baby may have some problems with the stress of normal labour.

A contraction stress test is usually done if you have an abnormal biophysical profile. A biophysical profile uses ultrasound during a non-stress 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 non-stress 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:	Carrie Henley Jan Nissl, RN, BS	Last Updated: May 15, 2006
Medical Review:	Joy Melnikow, MD, MPH - Family Medicine Deborah A. Penava, BA, MD, FRCSC, MPH - Obstetrics and Gynecology
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