A contraction stress test is a test for pregnant people. It measures your baby’s heart rate during labor contractions. In a contraction, your baby’s oxygen and blood supply temporarily drop. Most babies can handle this decrease. But if your baby’s heart rate stays low after a contraction, it could mean your baby will have problems with typical labor.
A contraction stress test (CST) is a test for pregnant people. It checks your baby for signs of stress during uterine contractions. During the test, your healthcare provider gives you a hormone that makes your uterus contract. These contractions are similar to labor contractions but typically don’t start labor.
During labor contractions, your baby’s blood and oxygen supply temporarily drop. Most babies can handle this decrease. But some babies’ heart rates lower even after the contraction is over. A CST simulates labor contractions to see if your baby can tolerate the drop in blood and oxygen.
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You usually only need a CST if you have atypical results after a nonstress test or biophysical profile:
During a nonstress test, your healthcare provider monitors your baby’s heart rate without putting any external stress on the baby. A contraction stress test measures your baby’s heart rate during the stress of uterine contractions.
Your healthcare provider typically performs a contraction stress test when you are 34 or more weeks pregnant.
In a contraction stress test, your healthcare provider gives you a hormone called oxytocin. Oxytocin causes your uterus to contract.
Your provider records your baby’s heart rate during and between contractions. If your baby’s heart rate slows after a contraction, it means your baby may be at risk for problems during labor contractions.
Your healthcare provider will give you specific instructions to prepare for a contraction stress test. Usually, you stop eating and drinking for four to eight hours before the test.
If you smoke, your provider will instruct you to stop at least two hours before your test. Smoking can decrease your baby’s heart rate and interfere with the test results.
Contraction stress tests are typically outpatient tests, meaning you can go home the same day. During the test:
Immediately after the test, your care team observes you until your contractions stop. If your contractions don’t stop, your provider may give you medicine to stop them. The test often takes up to two hours.
Contraction stress tests are typically safe tests. The biggest risk of the test is that it may cause you to go into labor before your due date.
People who are pregnant with multiples (twins, triplets or more babies) may not be candidates for contraction stress tests. If you’re pregnant with multiples, the test is more likely to induce labor.
A contraction stress test tells you whether your baby’s heart rate slows down:
If your test results are positive, it means your baby may be unable to tolerate the stress of labor contractions. Your healthcare provider may recommend additional tests, including another stress test a week or two later. If you continue to have positive results, your healthcare provider may recommend delivery via cesarean section.
Contraction stress tests measure your baby’s health at the time of the test. You may have several contraction stress tests in the last few weeks of your pregnancy. Your healthcare provider may schedule a weekly contraction stress test if your test results show that your baby may not be able to tolerate labor contractions.
A note from Cleveland Clinic
A contraction stress test measures your baby’s heart rate during uterine contractions. During contractions, your baby’s heart rate and oxygen supply are temporarily lower. Most babies can handle this temporary drop. If your baby’s heart rate stays low after the contraction, it could be a sign that your baby can’t tolerate the stress of labor contractions. If your test results are positive, your healthcare provider may recommend additional tests or cesarean delivery.
Last reviewed by a Cleveland Clinic medical professional on 04/26/2022.
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