What is a nonstress test?

A nonstress test is done during pregnancy. It measures the heart rate of the unborn baby (fetus) in response to its movements. In most cases, the heart rate of a healthy baby increases when the baby moves. The nonstress test is usually done in the last trimester (weeks 29 to 40) of pregnancy.

Why might I need a nonstress test?

Your healthcare provider may advise a nonstress test in any of these cases:

• Your pregnancy is high risk because you have diabetes, high blood pressure, a clotting or blood disorder, or thyroid, kidney, or heart disease

• Your baby is moving less than usual, has slow growth, has too much or too little amniotic fluid, or is overdue

• You had a stillborn baby in the past

• Your blood is Rh negative

• You are having 2 or more babies (multiple pregnancy)

What are the risks of a nonstress test?

There are no risks to either the mother or baby during a nonstress test.

How do I get ready for a nonstress test?

You don’t need to do any special preparation before the test.

What happens during a nonstress test?

The test may be done in a special prenatal testing area of the hospital. Or it may be done in your healthcare provider’s office.

The procedure may vary, but a typical nonstress test may go like this:

• You’ll lie in a comfortable position on an exam table. The provider puts gel on your belly. They put a belt around your belly. A device called a transducer is attached to the belt. It’s an external fetal heart rate monitor. The provider puts it over the baby’s heartbeat. 

• The baby’s heart rate is recorded on a monitor and on a paper printout.

• You’ll be asked to push a button on the monitor each time you feel your baby move.

• This test usually lasts for 20 to 40 minutes.

In some cases, the test takes place during a baby’s sleep cycle, when there is little fetal movement. A special sound (acoustic) device may be used to awaken the baby. It is placed against the mother’s belly and makes a noise like a buzzer. This isn’t harmful to the baby. But it may help a sleepy baby become more active. Your baby may also wake up if you eat or drink.

What happens after a nonstress test?

The provider will remove the belt and transducer and wipe off the gel. You’ll be told the results of the test. 

Test results of the nonstress test may be:

• Reactive (normal). The baby’s heart rate goes up 2 or more times in the testing period.

• Nonreactive. There’s no change in the baby’s heart rate when the baby moves. This may mean you’ll need other tests.

A nonreactive nonstress test doesn’t always mean your baby has a problem. The baby may simply be asleep or too immature. It’s common for preterm babies to have nonreactive nonstress tests, especially before 28 weeks. Your healthcare provider will tell you if you need other prenatal testing.

Next steps

Before you agree to the test or procedure make sure you know:

• The name of the test or procedure

• The reason you’re having the test or procedure

• What results to expect and what they mean

• The risks and benefits of the test or procedure

• What the possible side effects or complications are

• When and where you’re to have the test or procedure

• Who will do the test or procedure and what that person’s qualifications are

• What would happen if you didn’t have the test or procedure

• Any alternative tests or procedures to think about

• When and how you’ll get the results

• Who to call after the test or procedure if you have questions or problems

• How much you’ll have to pay for the test or procedure