McKesson Clinical Reference Systems: Women's Health Advisor 2002.2

What is a contraction stress test?

A contraction stress test is a way to test the health of an unborn baby. It checks the baby's heart rate when the mother has a uterine contraction. During this test, the baby's heart rate and the mother's contractions are recorded.

Most contractions decrease the flow of blood and oxygen to the baby for a short time. By observing the baby's heart rate during a contraction, your health care provider can tell if the baby is able to handle the stress of the contractions that occur during labor.

When is a contraction stress test used?

This test may be done if:

• During a nonstress test the baby's heart rate did not rise enough to be considered a reactive result.
• The biophysical profile score is low.
• Your health care provider knows or suspects that your baby or you have a high-risk condition.

Very often a biophysical profile (a combination of a nonstress test and an ultrasound scan) may be done instead of a contraction stress test.

How is a contraction stress test done?

You lie on a bed on your left side. Your health care provider places a strap with a pressure gauge around your abdomen. The gauge measures contractions of your uterus. An ultrasound transducer is placed over the area of your abdomen where the baby's heart is. It measures your baby's heart rate. The changes in pressure from the uterus (contractions) and the baby's heart rate are recorded as two lines on a graph.

For the test to be valid, you must have three 40-second uterine contractions in a 10-minute period. If, after a reasonable period, you haven't had three good contractions, you may be asked to stimulate your breasts by placing a warm compress on one of them or by rubbing a nipple. This causes the natural release of oxytocin, which can make your uterus contract. If these techniques don't cause enough good contractions, your health care provider may give you a very small amount of oxytocin through a vein (IV) until you have three contractions in 10 minutes.

How is the test interpreted?

• If the baby's heart rate does not fall during the contractions, the result of the test is negative, which is reassuring. It suggests that the baby is healthy.
• If the baby's heart rate falls during contractions, the test is considered positive, which is not reassuring. It means the baby may be having some problem and may have more serious problems during labor.

What happens after a contraction stress test?

The contraction stress test is usually repeated once or twice a week.

If you have a positive stress test, you will probably be admitted to the hospital. If your baby is having a problem that cannot be corrected, your health care provider may want to deliver the baby early with a cesarean section.

What are the risks of a contraction stress test?

The stress test can cause some women to start labor. For this reason it is not done if you are at risk of going into premature labor.

The test could cause too many uterine contractions, especially if you are given oxytocin to stimulate the contractions. Oxytocin is given slowly and carefully, but in some cases it can stimulate too many contractions and needs to be stopped.

Your health care provider also may not use this test if:

• You had a previous cesarean section with a vertical incision of the uterus.
• There is a chance that the placenta will separate from the uterus early. That is, your provider suspects you may have placental abruption.
• You have more than one baby in the uterus.
• The placenta is low in the uterus (placenta previa). This can cause massive bleeding.
• You have premature rupture of your membranes (your bag of waters has broken).

This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.