A contraction stress test checks to see if your baby (fetus) will be okay with the reduced oxygen levels that normally occur during contractions when you are in labor. The test includes external fetal heart monitoring (nonstress test). The test is done when you are 34 or more weeks pregnant.

During a uterine contraction, the blood and oxygen supply to your baby drops for a short time. This is not a problem for most babies. However, some babies get a slower heart rate. This change in heart rate can be seen on the external fetal monitoring device.

For a contraction stress test, the hormone oxytocin is given to you in a vein (intravenously, or IV) to cause labor contractions. You may also massage your nipples. This tells your body to release oxytocin. If your baby's heart rate slows down (decelerates) in a certain pattern instead of speeding up (accelerates) after a contraction, your baby may have some problems with the stress of normal labor.

A contraction stress test is usually done if you have an abnormal biophysical profile. A biophysical profile uses ultrasound during a nonstress test to measure a series of physical characteristics of your baby. During the test, uterine contractions, fetal breathing, fetal muscle tone, fetal movements, and amniotic fluid volume are measured. A contraction stress test gives a better picture of your baby's health than the nonstress test. You may have more than one contraction stress test during your pregnancy.

Some doctors may do a biophysical profile or a Doppler ultrasound test instead of a contraction stress test.

Why It Is Done

A contraction stress test is done to check:

• If your baby will be okay with the reduced oxygen levels that normally occur during contractions during labor.
• If the placenta is healthy and can support your baby.

A contraction stress test may be done when results from a nonstress test or a biophysical profile are not in the normal range.

How To Prepare

You may be asked to not eat or drink for 4 to 8 hours before the test. Empty your bladder before the test.

If you smoke, stop for 2 hours before the test because smoking lowers your baby's activity and heart rate.

You will be asked to sign a consent form before a contraction stress test. Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

How It Is Done

A contraction stress test may be done in your doctor's office or hospital by a family medicine doctor or an obstetrician and a trained laboratory technician or nurse. You usually do not need to stay overnight.