Contraction Stress Test (CST)

Medically Reviewed by Traci C. Johnson, MD on June 09, 2023
Written by R. Morgan Griffin
2 min read

Some women who have complications during their pregnancy need a CST, although the test is much less common than it once was. More often, you would get a nonstress test or a biophysical profile. If those results indicate a possible problem, your doctor may suggest a CST as a follow-up.

CSTs are very uncommon in women carrying twins, because it can trigger early labor.

The contraction stress test helps predict how your baby will do during labor. The test triggers contractions and registers how your baby's heart reacts. A normal heartbeat is a good sign that your baby will be healthy during labor.

You'll lie down with two belts around your belly. One measures your baby's heartbeat, and the other measures contractions. (If you’re having twins, you’ll have two belts to measure heartbeats.) To trigger contractions, your doctor may give you a dose of the drug oxytocin through an IV in your arm. Or your doctor may suggest that you rub your nipples through your clothing, which can start contractions. Then you wait while the monitors record contractions and your baby's heartbeat. The test takes about 2 hours. The contractions can be uncomfortable.

CST is usually safe, but it sometimes triggers early labor. The test is riskier for women who have placenta previa, a higher risk of uterine rupture, or who had a previous C-section. Your doctor will help you weigh the benefits and risks before the test.

If your baby's heart rate drops during contractions, it could be a sign of problems. Your doctor may suggest further testing. Sometimes, early delivery is the best option.

If your baby's heart rate stays normal during the test, that's an excellent sign. Still, your doctor may suggest that you take the test again later if other test results show a possible problem.

CST is better at ruling out problems than diagnosing them. Many women with abnormal results have perfectly healthy babies.

Women may get a contraction stress test at 32 weeks or later. Before that, the test may not be safe. The number of times you need the test depends on your situation. Ask your doctor.

Oxytocin challenge test, stress test

Nonstress test, biophysical profile