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Test Overview
A contraction stress test is done to monitor the condition of a fetus in the late stages of pregnancy, just before labor begins. It can be done during external fetal heart monitoring (nonstress test) to determine whether the fetus can tolerate the stress of normal labor (see Electronic Fetal Heart Monitoring).
During a uterine contraction, the blood and oxygen supply to the fetus temporarily decreases. This stress is not a problem for most fetuses. However, some fetuses cannot handle the stress, and they respond to the test with a particular slowed heart rate pattern. This change in heart rate can be picked up by the electronic devices used during external fetal monitoring.
During pregnancy, the body releases a hormone (called oxytocin) that causes labor contractions to begin. For a contraction stress test, oxytocin is given intravenously to the woman to start contractions. Alternatively, the test may be done by having the woman massage her nipples to prompt her body to release oxytocin. If the fetus's heart rate slows down (decelerates) in a certain pattern instead of speeding up (accelerates) after a contraction, the fetus may not be able to tolerate the stress of normal labor.
A contraction stress test is often done if a the fetus's heart rate is abnormal during external fetal heart monitoring (nonstress test). A contraction stress test is considered more accurate than the nonstress test for monitoring the condition of the fetus.
