Non-Stress Test (NST) in Pregnancy

An NST is a non-invasive test used in late pregnancy to check a baby's health

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As you approach the end of your pregnancy, your doctor may schedule a non-stress test (NST) to monitor the health of your developing baby. As the name indicates, NSTs cause no stress to the baby. Using an external monitor, a healthcare provider can evaluate the baby's heartbeat and movement, and even detect uterine contractions.

This common, non-invasive test is generally performed in the third trimester of pregnancy, but your doctor may recommend it earlier, especially in high-risk pregnancies.

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Reasons For an NST in Pregnancy

If your provider orders a non-stress test, don't panic. It doesn't necessarily mean something is wrong with you or the baby. An NST is just one tool prenatal care providers can use to assess the baby's movement and health and confirm the pregnancy is progressing appropriately.

Some of the most common reasons a doctor might order an NST include:

  • Your baby is moving less.
  • Your due date has passed.
  • There is too much or too little amniotic fluid.
  • Your blood type is Rh.
  • You are 35 or older.
  • You are carrying multiples.
  • You previously experienced a stillbirth.
  • You have certain health concerns, including diabetes, high blood pressure, or thyroid problems.

When Is a Non-Stress Test Done?

Fetal non-stress tests are most frequently ordered starting at week 32; however, they may be recommended earlier in some cases. In many high-risk pregnancies, NSTs range in frequency from every other week to as often as every day. The recommended frequency will depend upon the reason for the NST test and any health issues the parent or baby may be experiencing.

What to Expect During a Non-Stress Test

Non-stress tests usually take place right in your healthcare provider's office. To prepare, wear loose, comfortable clothing and eat a small snack. Babies often become active shortly after the pregnant parent has eaten. It's probably a good idea to use the restroom before getting started as well, as the test can last anywhere from 20 to 40 minutes.

While you are either seated comfortably in a chair or resting in a reclined position on a table, your provider will attach a device called a transducer to a belt around your belly. The transducer is a safe and painless device that monitors fetal heart rate.

The monitor records your baby's heart rate during uterine activity. Every time you feel the baby move, you'll push a button so the provider can track the fetal heart rate in conjunction with that movement. When the test is complete, the provider removes the equipment and provides the test results right away.

Risks of a Non-Stress Test

An NST test is a low-risk, painless, and non-invasive procedure. The biggest risk during an NST is a misinterpretation of the data. Always share any concerns with your provider before undergoing the test. They can reassure you about steps they are taking to prevent any risk to you or your baby.

If the Baby Doesn't Move During the NST

Don't panic if your baby doesn't move during the non-stress test. They may just be asleep. When that happens, your doctor may ask you to consume something with cocoa or caffeine to perk the baby up. The test may also be extended to give the baby time to wake up.

Non-Stress Test Results

Non-stress test are either reactive or non-reactive:

  • Reactive: The fetal heart rate goes up at least twice or more during the testing period. This is a normal result, indicating the baby is healthy.
  • Non-reactive: The fetal heart rate does not change when the baby moves. The provider may take steps to stimulate the baby and perform the NST test again, or they may order additional tests.

Other Late Pregnancy Testing

If your baby is not as responsive as expected during the fetal non-stress test, your provider may order additional tests, including a biophysical profile (BPP) or a pregnancy stress test, to gather more information.

The BPP includes a highly detailed ultrasound that allows the technician to measure and assess certain factors, including the baby's breathing, muscle tone, and movement. Depending upon the BPP results, the provider may order more tests or move forward with a cesarean section or induction.

A pregnancy stress test (also called a contraction stress test) is another tool to assess fetal well-being, specifically how the baby responds to contractions. This test is usually done in the hospital, during late pregnancy, or even in the early stages of labor.

During a pregnancy stress test, a drug called Pitocin is administered intravenously to initiate contractions. The baby's heart rate is monitored throughout the process. If the baby passes the stress test, you can usually wait for labor to begin on its own. Otherwise, it may be time for a cesarean section or induction.

A Word From Verywell

Every pregnancy is unique. The reasons a provider may order a non-stress test will vary from person to person. If you have questions about an NST, why it's needed, and what the results mean, don't hesitate to ask your doctor. The goal of all prenatal testing is always to reassure you and your providers that everything is going well and to address any issues as quickly as possible.

6 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Robin Elise Weiss, PhD, MPH
Robin Elise Weiss, PhD, MPH is a professor, author, childbirth and postpartum educator, certified doula, and lactation counselor.