Nonstress Test

What is a nonstress test (NST)?

A nonstress test (NST or fetal nonstress test) is a pregnancy screening that measures fetal heart rate and reaction to movement. Your pregnancy care provider performs a nonstress test to make sure the fetus is healthy and getting enough oxygen. It’s safe and painless, and gets its name because it puts no stress (nonstress) on you or the fetus.

During an NST, your provider is watching for the fetus’ heart rate as it moves. Just as your heart rate increases when you run, its heart rate should increase when it moves or kicks.

If the fetus’ heart rate doesn’t react to movement or it isn’t moving at all, it doesn’t mean something is wrong. It could mean the fetus doesn’t have enough oxygen, but this isn’t always the case. Your pregnancy care provider uses the results of a nonstress test to decide if they need to order additional testing or if inducing labor is necessary.

Why do you need a nonstress test during pregnancy?

Not everyone needs a nonstress test. Your pregnancy care provider orders a nonstress test to check fetal health. Some reasons they may do this include:

• You’re past your due date: You’re overdue once your pregnancy is past 40 weeks. Being past your due date can cause complications, even if your pregnancy is low-risk and healthy.
• Your pregnancy is high-risk: Reasons for a high-risk pregnancy could include chronic medical conditions like diabetes or high blood pressure. It means your provider monitors you and the fetus more closely during pregnancy.
• You don’t feel the fetus moving as much: If you feel a decrease in the amount the fetus moves, your provider may order an NST.
• The fetus measures small for its gestational age: If your provider believes the fetus isn’t growing properly, they may order an NST earlier in your pregnancy.
• You’re expecting multiples: If you’re having twins, triplets or more, your pregnancy is at risk for complications.
• You’re Rh negative: If the fetus is Rh positive, your body will make antibodies against their blood. This can cause serious complications.

When in pregnancy are nonstress tests done?

A nonstress test typically happens after 28 weeks of pregnancy. This is when fetal heart rate starts reacting to movements. Your pregnancy care provider orders an NST when they feel it’s necessary to check on the fetus’ health.

What is the difference between a nonstress test and a stress test?

A nonstress test measures the fetus’ heart rate to see if it changes when it moves or during uterine contractions (when muscles in your uterus tighten). An NST places no extra stress on you or the fetus. You wear monitors around your belly and lay down for the test.

A stress test measures your heart rate, blood pressure and oxygen levels under stress. It usually involves walking on a treadmill or pedaling on a stationary bike with monitors attached to your chest. The test helps your provider determine how well your heart responds when it’s working hard or under stress.

How does a nonstress test work?

A nonstress test typically follows these steps:

• You lie down on a reclined chair or exam table.
• Your provider attaches two elastic belts to your belly. Each belt has a sensor attached to it. One sensor monitors your contractions, even ones you can’t feel. The other monitors the fetus’ heart rate, which you’ll hear on a machine. This is similar to how you hear the fetus’ heartbeat at prenatal appointments.
• Your provider records this information for about 30 minutes. They get this data on a chart to read and analyze.
• The test ends once your provider gets the information they need.
• Your provider removes the belts from your belly and discusses your results with you.

If the fetus isn’t moving during the test, it could be asleep. Your provider may try waking it up using a small buzzer or noisemaker on your belly, similarly to how an alarm clock wakes you up from sleep. Sometimes drinking a sugary drink or eating a snack helps wake the fetus during a nonstress test.

How do I prepare for an NST?

You don’t have to prepare for an NST. Your provider may have you use the restroom first so your bladder is empty.

How long does a nonstress test take?

A typical NST takes about 30 minutes, although it could take longer.

What are the risks of a nonstress test?

There are no risks to a nonstress test. It’s safe for both you and the fetus.

When do you get the results from a nonstress test?

You’ll know your results right away. Your pregnancy care provider or obstetrician will discuss the results with you and what they mean before you leave.

What is a normal nonstress test (NST)?

Your results will be either reactive (reassuring) or nonreactive, and you’ll know your results shortly after the test.

Reactive NST

An NST is reassuring or reactive when the fetus’ heart rate accelerates (increases) when it moves or when you have a contraction. This means that fetal heart rate reacts to movement. It must react two times within a 20-minute testing period to get a reactive result.

Nonreactive

An NST is nonreactive when these accelerations don’t occur — the fetus’ heart rate doesn’t increase with movement or it doesn’t move at all. Additional tests can help determine why the fetus wasn’t active during the nonstress test. It could mean the fetus isn’t getting enough oxygen, or it could simply mean the fetus was extra sleepy. Medications you take can also cause nonreactive results.

It’s important to remember that a nonreactive nonstress test doesn’t mean something is wrong. It means there isn’t enough information, and you may need more tests.

Additional tests could include:

• Biophysical profile: A test that combines a nonstress test with an ultrasound.
• Contraction stress test: A test that measures how the fetus reacts to contractions. During the test, your healthcare provider gives you medication that makes your uterus contract. These contractions are similar to labor contractions but don’t start labor.

If test results determine the fetus is at risk for complications, you may need closer monitoring or an early delivery. This depends on how far along you are in your pregnancy.

Be sure to discuss your nonstress test results with your provider. They can explain your results and answer any questions you have.

What happens if the fetus doesn't move during NST?

Don’t worry if the fetus isn’t moving — it doesn’t mean there’s a problem. It could be that it’s sleeping or that it just isn’t cooperating that day. Your pregnancy care provider may use a buzzing device to wake the fetus and get it moving. You also may get a sugary drink or snack to eat, as this can also wake it up.

What does it mean to fail a nonstress test?

Nonstress tests don’t have a pass or fail result. However, the fetus can be nonreactive. Having a nonreactive result doesn’t mean the fetus is in trouble. It just means you may need more testing to find out why you had a nonreactive result.

Can a nonstress test detect the fetus' sex?

No, an NST doesn’t detect the fetus’ sex.

A note from Cleveland Clinic

A nonstress test (NST) helps your pregnancy care team determine if the fetus is healthy. An NST gives your provider information about fetal heart rate in response to movement. Your results are either reactive or nonreactive. While the test doesn’t put any stress on you or the fetus, it can cause you to worry. A nonreactive test doesn’t indicate problems, meaning more tests may be necessary. Talk to your provider if you have concerns about your nonstress test or what it means for your pregnancy. They can walk you through what’s going to happen and ease your worries.