A contraction stress test checks to see if your baby will stay healthy during contractions when you are in labor. This test includes external fetal heart monitoring . The test is done when you are 34 or more weeks pregnant.
During a contraction, the blood and oxygen supply to your baby drops for a short time. This is not a problem for most babies. But the heart rate of some babies gets slower. This change in heart rate can be seen on the external fetal monitor.
For this test, you are given the hormone oxytocin. This hormone causes uterine contractions. You may also massage your nipples. This tells your body to release oxytocin. During this test, your baby's heart rate may slow down (decelerate) in a certain pattern after a contraction instead of speeding up (accelerating). This means your baby may have problems with the stress of normal labor.
A contraction stress test is usually done if you have an abnormal nonstress test or biophysical profile. A biophysical profile uses ultrasound during a nonstress test to measure a series of physical traits of your baby. You may have more than one contraction stress test while you are pregnant.
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:
- Find out if your baby will stay healthy during labor, when contractions reduce the oxygen levels.
- Check to see if the placenta is healthy and can support your baby.
This 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. Smoking can lower your baby's activity and heart rate.
You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done.
Talk to your doctor if you have any concerns about 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 a hospital. It is done by a family medicine doctor or an obstetrician and a trained lab technician or nurse. You probably won't need to stay overnight.
During the test, you will lie on a bed with your back raised. You will be tilted a little to your left side. This is so you will not put pressure on the blood vessels in your belly. Two belts with sensors will be placed around your belly. One belt holds the sensor that records your baby's heart rate. The other sensor measures your contractions. Gel may be used on your skin with the heart rate sensors. The sensors are hooked to a recording unit. The heart rate monitor may be moved if your baby changes position.
Your baby's heart rate and your contractions are recorded for 10 minutes. Your blood pressure and other vital signs are also recorded.
You will be given the hormone oxytocin in a vein (intravenously, or IV). It is started at a low dose. The dose is increased until you have three contractions within 10 minutes that each last longer than 45 seconds. Or you may be asked to massage one of your nipples by hand to start contractions. If you don't have a second contraction within 2 minutes of the first, you will rub your nipple again. If contractions do not occur within 15 minutes, you will massage both nipples.
After the test, you will be watched until your contractions stop or slow down to what they were before the test. A contraction stress test may take 2 hours.
How It Feels
You may need to lie on your left side for the test. This position may not be comfortable when you are having labor contractions. The belts holding the sensors may bother you. Most women say this test is uncomfortable but not painful.
Using oxytocin also has risks.
- It may cause labor to start sooner than your expected delivery date.
- It may cause contractions that go on for a long time. This may cause problems with your baby. The contractions usually stop when the oxytocin is stopped. You may get a medicine to stop the contractions. In very rare cases, the contractions don't stop. If that happens, your doctor may suggest delivery.
A contraction stress test checks to see if your baby will stay healthy during contractions when you are in labor.
Results of the test tell your baby's health for 1 week. The test may need to be done more than once during your pregnancy.
Normal test results are called negative.
Your baby's heart rate does not get slower (decelerate) and stay slow after the contraction (late decelerations). Note: There may be a few times during the test when your baby's heart rate slows down. But if it doesn't stay slow, it isn't a problem.
Your baby is expected to be able to handle the stress of labor if there are no late decelerations in your baby's heart rate during three contractions in a 10-minute period.
Abnormal test results are called positive.
Your baby's heart rate gets slower (decelerates) and stays slow after the contraction (late decelerations). This happens on more than half of the contractions.
Late decelerations mean that your baby might have problems during normal labor.
What Affects the Test
You may not be able to have the test, or the results may not be helpful, if:
- You have had past pregnancy problems. Examples include a cesarean section with a midline (vertical) incision, placenta previa, or placenta abruptio. Experts do not recommend this test if you are pregnant with more than one baby or you are likely to have premature rupture of the membranes (PROM). The test also isn't recommended if you have an incompetent cervix or you have been given magnesium sulfate during your pregnancy.
- You have had a uterine surgery in the past. Strong contractions may cause the uterus to rupture.
- You smoke or use cocaine.
- Your baby is moving during the test. It may be hard for the sensors to record your baby's heart rate or contractions.
- You are very overweight.
What To Think About
- A contraction stress test may show that your baby's heart rate slows down (decelerates) when your baby is not actually having problems. This is called a false-positive result.
- Some doctors use oxytocin instead of nipple massage. Nipple massage can cause long, uncontrolled contractions.
Other Works Consulted
Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.
Handbook of Diagnostic Tests (2003). 3rd ed. Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
Primary Medical ReviewerSarah Marshall, MD - Family Medicine
E. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerWilliam Gilbert, MD - Maternal and Fetal Medicine
Current as ofAugust 11, 2015