What is a nonstress test?

A nonstress test (NST) is a safe and painless test for pregnant people. The test measures the heart rate of your developing baby as the baby moves or when you have contractions in your uterus. Your uterus is the place where your baby grows during pregnancy.

In most healthy babies, the heart rate, also known as the fetal heart rate, increases during movement. If your nonstress test results showed that the fetal heart rate was not normal, it may mean that your baby is not getting enough oxygen. If this happens, you may need more testing or treatment. In some cases, your health care provider may want to induce labor so you can deliver your baby. Your provider will give you medicine or use other methods to start labor before it begins naturally.

Other names: fetal nonstress test, NST

What is it used for?

A nonstress test is used to check your baby's health before birth. The test is usually done in the third trimester of pregnancy, most often after 28 weeks. A baby born between 39 and 41 weeks is considered full-term.

Why do I need a nonstress test?

Not all pregnant people need a nonstress test. But you may need this test if:

• Your baby doesn't seem to be moving as much as usual.
• Your pregnancy is overdue (at 42 weeks or beyond).
• You have a chronic medical condition that makes your pregnancy high risk, such as high blood pressure, diabetes, heart disease, or a clotting disorder.
• You had complications in a previous pregnancy.
• Your blood is Rh negative, and your baby's is Rh-positive, which is called Rh incompatibility. This condition can cause your immune system to attack your baby's red blood cells. 
• You are having more than one baby (twins, triplets, or more).

What happens during a nonstress test?

The test may be done in your provider's office or a hospital's prenatal area. It generally includes the following steps:

• You will lie on a reclining chair or exam table.
• Your provider will spread a special gel on the skin over your abdomen (belly).
• Your provider will attach two belt-like devices around your abdomen. One will measure your baby's heartbeat. The other will record your contractions.
• Your provider will move the device over your abdomen until the baby's heartbeat is found.
• The baby's heart rate will be recorded on a monitor, while your contractions are recorded on paper.
• You may be asked to press a button on the device each time you feel your baby move. This allows your provider to record the heart rate during movement.
• The test usually lasts about 20 minutes to 30 minutes.
• If your baby isn't active or moving during that period, they may be asleep. To wake up the baby, your provider may place a small buzzer or other noisemaker over your abdomen. This won't harm the baby but it may help a sleepy baby become more active. Your baby may also wake up if you have a snack or sugary drink.
• Your provider will remove the belts. They will likely review the results with you soon after the test.

The procedure is very safe. It's called a "nonstress" test because no stress, or risk, is placed on the baby during the test.

Will I need to do anything to prepare for the test?

You don't need to do any special preparations for a nonstress test. However, your provider may ask you to go to the bathroom to empty your bladder before the test.

Are there any risks to the test?

There is no risk to you or your baby from having a nonstress test.

What do the results mean?

Nonstress test results are given as one of the following:

• Reactive or Reassuring. This means your baby's heart rate increased two or more times during the testing period.
• Nonreactive. This means your baby's heartbeat didn't increase when moving or the baby wasn't moving much.

A nonreactive result doesn't always mean your baby has a health problem. Your baby may have been asleep and not easily awoken. Nonreactive results may also be caused by certain medicines taken during pregnancy. But if the result was nonreactive, your provider will probably take more tests to find out if there is cause for concern. If your baby is found to be at risk, you may need treatment or monitoring, or to have labor induced if it is late enough in your pregnancy.

If you have questions about your results, talk to your provider.

Is there anything else I need to know about a nonstress test?

Additional noninvasive tests to check your developing baby's heart rate and health can include:

• Biophysical profile. This test combines a nonstress test with an ultrasound. An ultrasound imaging test uses sound waves to create a picture. The ultrasound checks your baby's breathing, muscle tone, and amniotic fluid level.
• Contraction stress test. This test checks how your baby's heart reacts when your uterus contracts. To make your uterus contract, you may be asked to rub your nipples through your clothing or may be given a medicine called oxytocin, which can cause contractions.

These tests pose no known risks to you or your baby.