Contraction Stress Test
A contraction stress test checks to see if your baby will stay healthy during contractions when you are in labor. This test includes external electronic fetal monitoring. The test is done when you are 32 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 may be given the hormone oxytocin. This hormone causes uterine contractions. Or you may be asked to 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 normal.
How To Prepare
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 may be asked to sign a consent form that says you understand the risks of the test and agree to have it done.
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. Your blood pressure and other vital signs are also recorded.
You may be given the hormone oxytocin in a vein (intravenously, or I.V.). 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.
How long the test takes
A contraction stress test may take 2 hours.
How It Feels
You may have some discomfort during the contractions. And the belts that hold the sensors in place may feel tight on your belly. Most people say this test is uncomfortable but not painful.
Electronic fetal monitoring may show that your baby is having problems when your baby is healthy. It can't find every type of problem, such as a birth defect.
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.
Results of the test help predict if your baby will stay healthy during labor for the upcoming 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).
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.
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.