Contraction Stress Test

What is a contraction stress test?

A contraction stress test (CST) is a test if you’re pregnant. 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.

Who needs a contraction stress test?

You usually only need a CST if you have atypical results after a nonstress test or biophysical profile:

• Nonstress tests check your baby’s heart rate and oxygen supply. Healthcare providers perform nonstress tests around 28 weeks of pregnancy.
• Biophysical profiles use a nonstress test along with soundwave imaging (ultrasound). These tests look at your baby’s heart rate, breathing, muscles and movements.

What is the difference between a nonstress test and a contraction stress test?

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.

When is a contraction stress test performed?

Your healthcare provider typically performs a contraction stress test when you are 34 or more weeks pregnant.

How does a contraction stress test work?

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.

How do I prepare for a contraction stress test?

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.

What can I expect during a contraction stress test?

Contraction stress tests are typically outpatient tests, meaning you can go home the same day. During the test:

1. You lie on a bed with your back slightly elevated.
2. A nurse wraps two belts with sensors around your belly. One sensor measures your baby’s heart rate. The other records your contractions.
3. You receive oxytocin through an intravenous (IV) line. Your provider may ask you to massage your nipples to release more oxytocin to start contractions.
4. Your provider records your baby’s heart rate during contractions.
5. A nurse removes the IV to slow down or stop contractions.

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.

What are the risks of a contraction stress test?

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.

Who should not have a contraction stress test?

If you’re pregnant with multiples (twins, triplets or more babies), you may not be a candidate for a contraction stress test. The test is more likely to induce labor.

What do the results of a contraction stress test mean?

A contraction stress test tells you whether your baby’s heart rate slows down:

• Normal (negative) results mean your baby’s heart rate doesn’t stay slow after a contraction (late decelerations).
• Abnormal (positive) results mean your baby’s heart rate slows down and stays slow after a contraction.

What happens after a positive contraction stress test?

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.