Contraction Stress Test (CST): The Ultimate Guide

A contraction stress test is done to check how well the fetus is coping with contractions of childbirth. It’s usually done in the third trimester of pregnancy.

A contraction stress test is a medical procedure that is used to assess the health of the baby and the placenta during pregnancy. It is also used to determine the risk of premature delivery. In this guide, we will discuss how to perform a contraction stress test, what to expect, and what the results mean.

What is a contraction stress test?

A contraction stress test is done to check how well the fetus is coping with contractions of childbirth. It’s usually done in the third trimester of pregnancy but can be done earlier if there are concerns about the baby’s health.

During labor contractions, your baby’s blood and oxygen supply temporarily drop. Most babies can handle this decrease. But some babies’ heart rates lower even after the contraction is over. A CST simulates labor contractions to see if your baby can tolerate the drop in blood and oxygen.

The test is done by hooking the mother up to a fetal monitor and then inducing contractions. The contractions are usually not as strong as true labor contractions, but they can be uncomfortable. The baby’s heart rate is monitored during the contractions to see how well he or she is tolerating them.

Even though a CST is required for some expectant moms, it is now less frequent than it was formerly. Nonstress tests or biophysical profiles are more typical. If your doctor detects a potential issue through these tests, he or she may recommend a CST as a follow-up. You may have more than one contraction stress test while you are pregnant.

Why is a contraction stress test done?

The primary reason for having a CST is to check how well the baby is handling contractions during labor. If the baby’s heart rate drops with each contraction or doesn’t recover quickly after the contraction ends, it may be a sign of fetal distress. To make sure the placenta is healthy so that it can support your baby.

In some cases, a CST is done earlier in pregnancy if the mom has a medical condition that may affect the baby’s health.

A CST may also be done if the mom has had a previous baby with a heart condition or birth defect.

Who should not have a contraction stress test?

You may not be able to have a CST if

  • you are pregnant with twins or more
  • you have had a previous cesarean delivery
  • you are at risk for preterm labor or have had a previous premature delivery
  • you are on certain medications, such as beta-blockers
  • you have had a recent vaginal bleeding or ruptured membranes
  • you have placenta previa, vasa previa, cervical incompetence, or any contraindication to labor

How do I prepare for a contraction stress test?

You don’t need to do anything special to prepare for a CST. You may be instructed to refrain from eating or drinking for 4 to 8 hours before the test. Before the examination, empty your bladder.

You’ll be asked to sign a consent form that acknowledges the dangers of the examination and agrees to have it performed.

What happens during a contraction stress test?

A contraction stress test may be done in your doctor’s office or a hospital. You’ll be asked to lie on your back tilted a little to your left side on an exam table. 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.

You’ll be given an IV, and a medication called oxytocin (Pitocin) would be slowly injected through the IV. The oxytocin will cause contractions that are similar to labor contractions. The contractions will usually start within 15 minutes.

The dosage is increased until you have three or more contractions in 10 minutes that each last greater 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.

Your baby’s heart rate will be monitored during the contractions. The test will last for about 20 to 30 minutes.

You may feel some discomfort during the contractions, but they shouldn’t be too painful. The baby’s heart rate will be monitored throughout the test.

When the test is over, the contractions will stop, and you can go home.

What happens after a contraction stress test?

You should be able to go about your normal activities after a CST. Drink plenty of fluids and rest when you can.

If your doctor detects any problems during the test, he or she may recommend further testing or monitoring. In some cases, you may need to be hospitalized for closer monitoring.

Results of CST

Negative test results

Normal test results are called negative, when your baby’s heart rate does not slow (decelerate) after the contraction and it doesn’t remain low (late decelerations). Your baby’s heart rate may slow down a few times throughout the procedure. But if it doesn’t stay that way, it isn’t an issue.

Your baby is expected to be able to deal with labor stress if there are no late decelerations in his or her heart rate during three contractions.

Positive test results

Abnormal test results are called positive, when the heart rate of your newborn drops (decelerates) and remains this way after the contraction (late decelerations). This occurs on more than half of the contractions during the test. Late decelerations mean that your baby might have problems during normal labor.

What happens after a positive contraction stress test?

If your baby’s test results are positive, this implies he or she may be unable to deal with the strain of labor contractions. Your doctor may recommend further testing. If you continue to have positive results, your healthcare provider may recommend delivery by cesarean section.

What are the risks of a contraction stress test?

There are very few risks associated with a CST. In some cases, the contractions may be strong and uncomfortable. If this happens, the test can be stopped at any time.

Sometimes, contractions may 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 medicine to stop the contractions. In very rare cases, the contractions may cause the baby’s heart rate to drop too low. If this happens, the baby may need to be delivered immediately and leading to premature birth.

If you have any concerns or questions about a CST, be sure to talk to your doctor.

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