How a Contraction Stress Test Works

Female doctor touching pregnant patient's belly

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The contraction stress test (CST) is a test to see how your baby might cope with contractions during labor. If recommended, the test is typically done near the end of pregnancy.

To perform the test, your doctor will induce mild contractions. An external fetal monitor, which is strapped to your abdomen during the test, keeps track of the strength of the contractions and your baby’s heartbeat.

Also Known As

  • Pregnancy stress test
  • Stress test
  • Oxytocin challenge test (OCT)

Reasons for a Contraction Stress Test

Contraction stress tests (CST) are one way to monitor the health of a fetus before labor. A CST may be part of a series of tests you undergo. Other common late-stage pregnancy monitoring includes a non-stress test (NST) and a biophysical profile (BPP)

The goal of all late-stage pregnancy tests is to assess whether a fetus is at risk for stillbirth. If the results of CSTs are not reassuring, doctors can intervene prior to labor. 

Your doctor might suggest a CST if:

  • You have a high-risk pregnancy
  • You have diabetes
  • You have had complications in a previous pregnancy
  • Your pregnancy has gone past 40 weeks
  • The results of an NST or BPP are abnormal

Since a CST can sometimes jump-start labor, it is not recommended for people who are at risk for preterm labor or for people who have placenta previa

What to Expect During the Test

A CST is done near the end of pregnancy, usually at 34 weeks or later. The test is often done in the hospital. 

During the test, your doctor will place two straps over your abdomen—one to measure contractions, the other the measure fetal heart tones. Your doctor will administer Pitocin (artificial oxytocin) to induce contractions. Alternately, you may stimulate your nipples by rubbing them, which can also bring on contractions.

Your doctor will be looking for a frequency of three contractions every 10 minutes. Your doctor might need to increase the Pitocin until your body responds with contractions that are frequent enough. The test itself may last a couple of hours from start to finish. After the nurse discontinues the medication, they will keep an eye on you until your contractions stop.

CST Results

CST results may be positive or negative. They may also be uncertain. When test results aren’t clear, your doctor may want to repeat the test in a couple of days:

  • Positive: Abnormal findings indicate a fetal heart rate that slows down and stays slow after the contraction for more than half of the contractions.
  • Negative: A normal test shows fetal heart tones that do not decelerate during or after contractions.
  • Equivocal: Results of the test are sometimes unclear.
  • Unsatisfactory: There may not be sufficient contractions to produce a quantifiable result.

The results of the CST last for one week. If your test is negative and your pregnancy continues beyond a week since your previous CST, your doctor may want to repeat the CST in a few days to a week.

Studies have found a positive result to be a valuable predictor of abnormal fetal heart rate patterns during delivery. If the results of the CST are positive, your doctor may suggest options for induction or cesarean birth.

Risks of a Stress Test in Pregnancy

A CST offers valuable information, but it does carry some risks. Your doctor will discuss the risks and benefits of CST with you. 

Risks of CST include:

  • Possibility of jump-starting labor
  • Pitocin may cause fetal distress
  • Discomfort

Hospital staff will closely monitor you during and after the test. If you are at risk for preterm labor or have placenta previa, a CST may not be recommended.

Stress Test Alternatives

If you are unable to have a CST, your doctor may use a combination of other fetal monitoring options to assess your baby’s well-being, including:

  • Non-stress test (NST)
  • Biophysical profile (BPP)
  • Doppler ultrasound exam

Frequently Asked Questions

What is the difference between a non-stress test and a contraction stress test?

A non-stress test monitors a fetus without inducing contractions. A contraction stress test, on the other hand, monitors a fetus’ response to contractions. During a CST, mild contractions are induced either through nipple stimulation or medication.

How often is a contraction stress test done?

If results are negative or inconclusive, your doctor may want to repeat the test weekly or twice a week until birth.

A Word From Verywell

If you are facing a CST, you may be feeling anxious. Rest assured that these tests have been used for decades and are considered safe. The test itself usually only produces mild discomfort. 

Talk to your doctor about any questions or concerns that you have about the test. Ask them about what the results could mean and what the next steps are. You may want your partner or doula to accompany you to the test for reassurance and support. 

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Article Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. Department of Medicine, MedlinePlus. Monitoring your baby before labor. Updated March 31, 2020.

  2. Michigan Medicine University of Michigan. Contraction stress test. Updated October 8, 2020.

  3. American College of Obstetricians and Gynecologists. Special tests for monitoring fetal well-being. Updated May 2019.

  4. Różańska-Walędziak A, Czajkowski K, Walędziak M, Teliga-Czajkowska J. The present utility of the oxytocin challenge test-a single-center study. J Clin Med. 2020;9(1). doi:10.3390/jcm9010131

Additional Reading
  • Gabbe, S, Niebyl, J, Simpson, JL. Obstetrics: Normal and Problem Pregnancies, 6th Edition.

  • Simkin, P and Ancheta, R. Wiley-Blackwell. The Labor Progress Handbook, 2nd Edition.