The Importance of Contraction Stress Test in High-Risk Pregnancies – 2023

A Contraction Stress Test (CST), also known as an Oxytocin Challenge Test, is a diagnostic test routinely used in obstetrics to evaluate fetal well-being during pregnancy. CST records the fetal heart rate response to uterine contractions induced by oxytocin or nipple stimulation. This enables the healthcare provider to evaluate the fetus’s ability to tolerate the stresses of labor.

The purpose of this article is to provide an overview of the Contraction Stress Test’s purpose, procedure, risks, and alternatives to help expectant mothers and healthcare providers make informed decisions about the use of CST in managing pregnancy.

Introduction to Contraction Stress Test (CST)

What is a Contraction Stress Test?

A contraction stress test (CST) is a diagnostic test that assesses the ability of the fetus to tolerate stress during contractions. The test involves monitoring the fetal heart rate and uterine contractions to evaluate the oxygen supply to the fetus during labor.

Why is a Contraction Stress Test Performed?

A CST is typically performed when there are concerns about fetal well-being, such as decreased fetal movement, vaginal bleeding, or a pregnancy that has gone past the due date. The test can help detect fetal distress and prevent potential complications during delivery.

Purpose of Contraction Stress Test

Detecting Fetal Distress

The primary purpose of a CST is to detect fetal distress, which can occur when the fetus is not receiving enough oxygen during contractions. Fetal distress can lead to serious complications, including brain damage or stillbirth.

Evaluating Uteroplacental Insufficiency

A CST can also evaluate uteroplacental insufficiency, which occurs when the placenta is not providing enough oxygen and nutrients to the fetus. This can be caused by conditions such as preeclampsia, gestational diabetes, or placental problems.

Procedure for Contraction Stress Test

Preparation for the Test

Before the test, the healthcare provider will explain the procedure and obtain consent from the patient. The patient will lie on her back while a fetal monitor is placed on her abdomen to measure the fetal heart rate. The patient’s contractions will also be monitored using a tocodynamometer or by palpation.

Conducting the Test

During the test, the healthcare provider will induce contractions using oxytocin or nipple stimulation to simulate natural labor. The fetal heart rate and contractions will be monitored for 10-20 minutes to evaluate the response of the fetus to stress.

Non-Stress Test vs. Contraction Stress Test

A non-stress test (NST) is a similar test that evaluates fetal well-being by monitoring the fetal heart rate in response to fetal movement. However, a CST is more sensitive and specific in detecting fetal distress, as it assesses the fetus during contractions when the oxygen supply is decreased.

Interpretation of Contraction Stress Test Results

Normal Results

A normal CST result indicates that the fetus is able to tolerate stress during contractions and is at low risk for complications during delivery.

Abnormal Results

An abnormal CST result indicates that the fetus is experiencing distress during contractions and may require further monitoring or intervention. The healthcare provider may recommend delivery or further testing, such as a biophysical profile or ultrasound.

False-Positive and False-Negative Results

CSTs can sometimes result in false-positive or false-negative results. A false-positive result indicates that the test suggests fetal distress when there is none, while a false-negative result suggests that the test did not detect fetal distress when there is one.

False-positive results can occur if the woman is dehydrated or if there are other factors affecting uterine contractions. False-negative results may occur if the contractions induced during the test are not strong enough to cause stress on the fetus.

Is a Contraction Stress Test Safe?

Yes, a CST is considered safe for both the mother and baby. The test is non-invasive and typically does not cause any harm to the baby. However, as with any medical procedure, there are some risks involved. The most common risks include:

  • Contractions that are too strong or too frequent
  • Temporary changes in fetal heart rate
  • Preterm labor or premature rupture of membranes

Risks and Complications of Contraction Stress Test

The contraction stress test (CST) is a commonly used diagnostic tool to assess fetal well-being during pregnancy. However, like any medical procedure, it carries some risks and potential complications. Before undergoing the test, it’s essential to understand the possible risks involved.

Minor Risks

The minor risks associated with CST include mild to moderate uterine contractions and potential discomfort during the procedure. In some cases, the test can cause false-negative or false-positive results, which may lead to unnecessary interventions or missed complications.

Major Risks

The major risks associated with CST are rare but can be severe. They include premature rupture of membranes, preterm labor, placental abruption, and fetal distress. If any of these complications occur, immediate medical intervention is necessary.

Alternatives to Contraction Stress Test

If the risks associated with CST are too high or a woman is unable to undergo the test for any reason, there are several alternatives available:

Biophysical Profile

The biophysical profile (BPP) is a non-invasive diagnostic test that assesses fetal well-being using ultrasound and fetal heart rate monitoring. It evaluates fetal breathing movements, fetal tone, amniotic fluid volume, and fetal heart rate reactivity.

Doppler Ultrasound

Doppler ultrasound is another non-invasive test that uses sound waves to measure blood flow in the umbilical cord and other fetal blood vessels. Abnormal blood flow can indicate potential complications such as fetal distress.


Amniocentesis is an invasive diagnostic test that involves taking a small sample of amniotic fluid from the uterus. The fluid is then analyzed for genetic abnormalities, fetal maturity, and infection.

Conclusion and Recommendations for Contraction Stress Test Use


The contraction stress test is a valuable diagnostic tool that can help detect potential fetal complications during pregnancy. However, it’s essential to weigh the risks and potential complications associated with the test before deciding to undergo it.

Recommendations for CST Use

Women who are at high risk for fetal complications or have certain medical conditions may benefit from CST. However, it’s essential to discuss the risks and benefits of the test with a healthcare provider before undergoing it. If the risks associated with CST are too high, there are several alternatives available that can still provide important information about fetal well-being.

In conclusion, the Contraction Stress Test is a valuable tool for monitoring fetal well-being during pregnancy. Although it is a safe test, there are potential risks that need to be considered. Therefore, it is crucial to discuss the benefits, risks, and alternatives with your healthcare provider to determine the most appropriate course of action. By doing so, expectant mothers can ensure they receive the best possible care for themselves and their unborn babies.


1. Is the Contraction Stress Test safe?

The Contraction Stress Test is generally considered a safe test. However, there are potential risks associated with it, such as uterine contractions leading to preterm labor, fetal distress, and placental abruption. Your healthcare provider will weigh the risks and benefits of this test based on your medical history and pregnancy status.

2. How long does the Contraction Stress Test take?

The CST typically takes around 60-90 minutes to complete. The procedure involves monitoring the fetal heart rate response to contractions, which can take some time to achieve.

3. Can I eat or drink before the Contraction Stress Test?

It depends on your healthcare provider’s instructions. Some providers may ask you to avoid eating or drinking for several hours before the test to prevent stomach discomfort. However, others may encourage you to eat a light meal before the test to stimulate uterine contractions.

4. What happens after an abnormal Contraction Stress Test?

If the CST results are abnormal, additional tests or interventions may be necessary, depending on the severity of the fetal distress. The healthcare provider may recommend further monitoring of the fetal heart rate, additional tests, or early delivery if necessary.

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