Why you may have a non-stress test in pregnancy

What is a non-stress test?

This simple, painless procedure is done during pregnancy to evaluate your baby's condition. It's called a non-stress test because it doesn't place any stress on your baby.

During the non-stress test (NST), your healthcare practitioner or a technician monitors your baby's heartbeat. Just as your heart beats faster when you're active, your baby's heart rate should go up while they're moving or kicking.

The test is typically done if you've gone past your due date, or in the month or two leading up to your due date if you're having a high-risk pregnancy.

Here are some reasons you might have a non-stress test:

• You have diabetes that's treated with medication, heart disease, or some other medical condition that could affect your pregnancy.
• You have gestational hypertension or preeclampsia.
• Your baby appears to be small or not growing properly.
• Your baby is less active than normal.
• You have too much amniotic fluid (polyhydramnios) or too little amniotic fluid (oligohydramnios).
• You've had a procedure such as an external cephalic version (to turn a breech baby) or third trimester amniocentesis. Afterward, your practitioner will order a non-stress test to make sure that your baby's doing well.
• You're past your due date and your practitioner wants to see how your baby is holding up during their extended stay in the womb.
• You've previously lost a baby in the second half of pregnancy, for an unknown reason or because of a problem that might happen again in this pregnancy. In this case, non-stress testing may start as early as 28 weeks.
• You have a multiples pregnancy with certain complications.
• Your baby has been diagnosed with an abnormality or birth defect and needs to be monitored.

What happens during a fetal non-stress test?

The non-stress test may be done at your caregiver's office or in a hospital.

You may be advised to eat a meal just before the test in the hope that eating will stimulate your baby to move around more. Although there's no hard evidence that this works, it can't hurt. It's also a good idea to use the bathroom before the test, because you may be lying strapped to a monitor for up to an hour.

During the procedure, you lie on your left side, possibly with a wedge under your back that allows you to lean back. Your blood pressure will be monitored at regular intervals.

A technician straps two devices to your belly: One monitors your baby's heartbeat, and the other records contractions in your uterus. The technician listens to and watches your baby's heartbeat on an electronic screen while your contractions are recorded on paper.

In some cases, you'll be asked to press a button when you feel the baby move. The test usually takes 40 to 60 minutes.

What do NST results mean?

Reactive (normal) result.

If your baby's heart beats faster (at least 15 beats per minute over his resting rate) for at least 15 seconds on two separate occasions during a 20-minute span, the result is normal, or "reactive." Some providers will refer to this as 15x15. (If you are before 32 weeks of your pregnancy, the goal is 10 beats above baseline for 10 seconds. Providers may refer to this as 10x10.)

A normal NST result is reassuring and means that your baby is probably doing fine for now. Your practitioner may want to repeat the test every week (or more often) until your baby's born.

If your baby's heart doesn't beat faster on two occasions as described above, the result is "nonreactive." A nonreactive result doesn't necessarily mean something is wrong. It just means that the test didn't provide enough information and you may need to take it again in an hour.

If your baby's NST isn't reactive, they could be asleep. You might be asked to drink some water, juice, or soda to get your baby going, or the technician may nudge them gently through your abdomen or try to wake them with a buzzer.

What if my non-stress test results aren't reassuring?

If you get a nonreactive result, your practitioner may recommend other tests such as a biophysical profile or contraction stress test.

But if your practitioner thinks that your baby's no longer doing well in the womb, they'll probably decide to induce labor or admit you to the hospital for prolonged observation.

Learn more:

• Group B strep screening
• Signs of labor
• Stages of labor