Nonstress Test (NST)

Medically Reviewed by Dan Brennan, MD on August 09, 2022
Written by R. Morgan Griffin
3 min read

The nonstress test (NST) is a simple, noninvasive way of checking on your baby's health.

The test, sometimes called a cardiotocography, records your baby's movement, heartbeat, and contractions. It notes changes in heart rhythm when your baby goes from resting to moving, or during contractions if you're in labor. Your baby's heart should beat faster when active -- just like yours. The NST can reassure you that your baby is healthy and getting enough oxygen.

It's called a nonstress test because the test won’t bother your baby. Your doctor won't use medications to make your baby move. The NST records what your baby is doing naturally.

NST is a common test for pregnant women. Your doctor may use it to check the health of your baby after weeks 26 to 28 of pregnancy. Certain results may mean your doctor needs to monitor your baby, do more tests, or schedule delivery. You may need an NST if:

  • You’re overdue
  • You have complications during pregnancy, especially if you’re pregnant with more than one baby
  • You had complications with a past pregnancy
  • Your baby seems to be moving less than usual
  • You have some medical conditions, such as high blood pressure, diabetes, or heart disease
  • You have Rh (rhesus) sensitization, a condition in which your blood type and the baby’s don’t match
  • You have low levels of amniotic fluid

The NST is safe for you and your baby. Your doctor will take your blood pressure before the test. Then, you'll lie down with two belts around your belly. One measures your baby's heartbeat and the other measures contractions. (If you’re carrying twins, you’ll have two belts to check their heartbeats.) Your doctor will check your blood pressure from time to time while they test your baby.

When you feel the baby kick or move, you may press a button so your doctor can see how the baby's heartbeat changed while moving. The test will take about 20 minutes.

If your baby seems to be sleeping, a nurse may try to wake up your baby by ringing a bell, moving your belly, or by using an acoustic stimulator.

A normal NST shows that your baby is getting enough oxygen and is doing well. If the results are unusual, your doctor may suggest further testing.

You can get one of two results from an NST:

Reactive: This result means that your baby’s heart rate went up to the expected level at least twice during the test.

Nonreactive: This means your baby’s heart rate didn’t rise as much as expected during the test. It doesn't necessarily mean there’s a problem. You can get this result if your baby is asleep. If your test is nonreactive your doctor may do other tests.

If your baby doesn't move during the NST, try not to worry. Many women with nonreactive results turn out to have perfectly healthy babies. Sometimes, babies sleep through the whole thing. The test is not checking "movement," but evaluating reactivity of the heartbeat. There may or may not be appreciable movement during the test.

You might start getting weekly or twice weekly nonstress testing after 28 weeks if you have a high-risk pregnancy. (Before 28 weeks, the test isn't accurate.) You may only need one isolated NST if the baby is not moving well. You may need the test more often depending on your situation. Ask your doctor.

A test similar to the NST is the contraction stress test. Your doctor may suggest you have this test if you are 34 weeks or more pregnant, and you’ve had a nonreactive result with a NST.