Fetal Nonstress Test (NST) During Pregnancy
Everything You Need to Know About a Nonstress Test
February 28, 2019

Everything You Need to Know About a Nonstress Test

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Everything You Need to Know About a Nonstress Test.
Everything You Need to Know About a Nonstress Test

At some point, your OB may order a nonstress test (a.k.a. NST) to check on your growing baby. Despite this test’s name, getting tested for things during pregnancy can be stressful, so we’ve decided to demystify the NST for you. Here’s the whole story on the nonstress test.

What is an NST?

A nonstress test is used to check in on a baby’s well-being while in utero. It measures the baby’s heart rate in response to their own movements. This lets doctors know whether the baby is getting the right amount of oxygen in there. Super important.

It’s called a nonstress test because it doesn’t cause any stress to your baby—plus, it’s noninvasive to you, so there’s not much to worry about. (Phew.)

For the NST, you’ll have to wear two belts with sensors on them around your belly. One sensor picks up baby’s heart rate, which will get recorded by a machine. The other will sense your contractions. This may be done at your healthcare provider’s office or the hospital.

The NST takes as little as 20 minutes but may take an hour or more, depending on how responsive your baby is.

When is an NST Performed?

The nonstress test is given after 26 weeks pregnant to 28 weeks pregnant—since after this is when baby’s heartbeat starts to get stronger with movement. And it may be ordered any time there’s reason to believe your baby’s at higher risk for not having enough oxygen. This may include:

  • Health conditions: If you have type 1 diabetes, heart disease or high blood pressure during pregnancy, the doctors may want to keep a close eye on your baby.
  • Past complications: Same goes for when there have been complications in a previous pregnancy. A nonstress test can give you extra peace of mind that your baby’s OK.
  • Rh incompatibility: If your blood is Rh negative and baby’s is Rh positive and this isn’t your first pregnancy, the doctors may want to monitor baby using a nonstress test.
  • Low amniotic fluid: If amniotic fluid is low (known as oligohydramnios), a nonstress test can be used to check on baby.
  • Decreased movement: If a baby hasn’t been moving around as often as usual, a nonstress test can help gauge if there’s cause for concern.
  • Pregnancy with multiples: If you’re pregnant with twins or more and have one or more pregnancy complications, you may get an NST.
  • Overdue: Went past your due date? An nonstress test may be ordered to check that baby’s still doing well while you wait for their much-anticipated arrival.

In many cases, the NST may be given as part of a biophysical profile, which also includes an ultrasound to check that baby’s looking healthy all-around.

Nonstress Test Results

Wondering how to read a nonstress test? Well, there are two results you can get:

Reactive nonstress test (NST): If during 20 minutes, your baby’s heart rate accelerates a certain amount two or more times, they’re considered “reactive,” meaning there’s no cause for concern. If they don’t have two of those accelerations in 20 minutes—don’t freak out. They might just be sleeping. You’ll have to stick around for at least 20 more minutes or maybe even 40 or longer though. And you may get extra stimulation—sound waves projected over your belly—to try to wake baby and get a reaction.

Non-reactive nonstress test (NST): If your baby’s non-reactive—meaning the heart rate didn’t speed up as desired two or more times in any of the 20-minute windows—it could be because they were sleeping or because of medications you’re taking. In some cases, problems with the placenta or umbilical cord could be causing low oxygen levels, which could make the baby non-reactive.

What happens if you get a non-reactive NST result? If you’re full-term, the doctor might recommend delivering your baby right away. If you’re not full-term, follow-up tests will probably be ordered to figure out why baby’s not reacting. If the nonstress test is read in context of the biophysical profile, other factors will be taken into account as the doctors evaluate your baby’s health.

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