Nonstress Test

A nonstress test (NST or fetal nonstress test) is a pregnancy screening that measures fetal heart rate and how it responds to movement. Your pregnancy care provider does this test to make sure the fetus is healthy and getting enough oxygen. A nonstress test typically happens after 28 weeks of pregnancy.

During an NST, your provider watches the fetus’s heart rate as it moves. Just as your heart rate increases when you run, the fetal heart rate should increase when the fetus moves or kicks.

If the fetal heart rate doesn’t change with movement, it doesn’t mean something is wrong. Your pregnancy care provider uses the results of a nonstress test to decide if they need to order more tests or induce labor.

When do you need one?

Not everyone needs a nonstress test. Your pregnancy care provider orders a nonstress test when:

• 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 medical conditions, like diabetes or high blood pressure. It means that your provider monitors you more closely during pregnancy.
• You don’t feel movement: Your provider may recommend an NST if you don’t feel the fetus move or feel it move less.
• The fetus measures small for its age: Your provider may order an NST if the fetus isn’t growing as expected.
• You’re expecting multiples: Your pregnancy is at risk for complications if you’re pregnant with multiples.
• You’re Rh negative: If the fetus is Rh positive, your body will make antibodies against their blood. This can cause serious complications.

How does a nonstress test work?

A nonstress test typically follows these steps:

1. You lie down on a reclined chair or exam table.
2. Your provider attaches two elastic belts to your belly. Each belt has a sensor attached to it. One sensor monitors your contractions, even those you can’t feel. The other monitors the fetal heart rate, which you’ll hear on a machine.
3. Your provider records this information for about 30 minutes. They get this data on a chart to read and analyze.
4. The test ends once your provider gets the information they need.
5. 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. This is like how an alarm clock wakes you up from sleep. Sometimes, drinking a sugary drink or eating a snack helps the fetus move, too.

How do I prepare for an NST?

You don’t have to prepare for an NST. Your provider may have you use the bathroom first so your bladder is empty. It helps to wear comfortable clothing so you can lift your shirt easily. You should also be prepared to sit or lie down for at least 30 minutes.

How long does it take?

A typical NST takes about 30 minutes, though it may take longer. This can happen if there isn’t much movement or if there are issues picking up the heartbeat signal. In some cases, your provider may also want more time to gather information. They may decide to extend the NST so that they feel confident about the results.

Risks of an NST

A nonstress test is safe and painless. It gets its name because it puts no stress (nonstress) on you or the fetus.

When do you get the results from a nonstress test?

You’ll know your results the same day. Your pregnancy care provider or obstetrician will discuss them with you and explain what they mean before you leave. If the results aren’t clear, you may need more monitoring or another test.

What is a normal nonstress test (NST)?

Your results will be either reactive (also called reassuring) or nonreactive. You’ll know them shortly after the test ends. The results of an NST aren’t given as positive or negative, or as pass or fail.

Reactive NST

An NST is reactive (reassuring) if the fetal heart rate accelerates (increases) when the fetus moves or when you have a contraction. This means the fetus is reacting to movement. It must react two times within a 20-minute testing period to get a reactive result. A reactive result means the test was normal.

Nonreactive NST

An NST is nonreactive if these accelerations don’t happen — the fetal heart rate doesn’t increase with movement, or the fetus doesn’t move at all. Additional tests can help your provider figure out why this may have happened.

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: This is a test that combines a nonstress test with an ultrasound.
• Contraction stress test: This is 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 don’t start labor.

If your NST results determine that 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 a 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 just not cooperating that day. Your pregnancy care provider may use a buzzing device to wake it up and get it moving. You may also get a sugary drink or snack.

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

An NST measures fetal heart rate to see if it changes with movement. You wear monitors around your belly for the test.

A stress test measures your own heart rate during physical activity. It usually involves walking on a treadmill or pedaling on a stationary bike with monitors attached to your chest.