A nonstress test (NST) is a test in pregnancy that measures fetal heart rate in response to movement and contractions. Results are either reactive or nonreactive. Nonreactive results don’t mean there’s a problem, but they can mean more tests may be necessary.
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.
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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:
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.
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.
A nonstress test typically follows these steps:
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.
You don’t have to prepare for an NST. Your provider may have you use the restroom first so your bladder is empty.
A typical NST takes about 30 minutes, although it could take longer.
There are no risks to a nonstress test. It’s safe for both you and the fetus.
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.
Your results will be either reactive (reassuring) or nonreactive, and you’ll know your results shortly after the test.
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.
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.
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.
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.
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.
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.
Last reviewed by a Cleveland Clinic medical professional on 10/04/2022.
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