Why do they do stress test during pregnancy

Reviewed by Neha Pathak, MD on March 19, 2021

Some women who have complications during their pregnancy need a CST, although the test is much less common than it once was. More often, you would get a nonstress test or a biophysical profile. If those results indicate a possible problem, your doctor may suggest a CST as a follow-up.

CSTs are very uncommon in women carrying twins, because it can trigger early labor.

The contraction stress test helps predict how your baby will do during labor. The test triggers contractions and registers how your baby's heart reacts. A normal heartbeat is a good sign that your baby will be healthy during labor.

You'll lie down with two belts around your belly. One measures your baby's heartbeat, and the other measures contractions. (If you’re having twins, you’ll have two belts to measure heartbeats.) To trigger contractions, your doctor may give you a dose of the drug oxytocin through an IV in your arm. Or your doctor may suggest that you rub your nipples through your clothing, which can start contractions. Then you wait while the monitors record contractions and your baby's heartbeat. The test takes about 2 hours. The contractions can be uncomfortable.

CST is usually safe, but it sometimes triggers early labor. The test is riskier for women who have placenta previa, a higher risk of uterine rupture, or who had a previous C-section. Your doctor will help you weigh the benefits and risks before the test.

If your baby's heart rate drops during contractions, it could be a sign of problems. Your doctor may suggest further testing. Sometimes, early delivery is the best option.

If your baby's heart rate stays normal during the test, that's an excellent sign. Still, your doctor may suggest that you take the test again later if other test results show a possible problem.

CST is better at ruling out problems than diagnosing them. Many women with abnormal results have perfectly healthy babies.

Women may get a contraction stress test at 32 weeks or later. Before that, the test may not be safe. The number of times you need the test depends on your situation. Ask your doctor.

Oxytocin challenge test, stress test

Nonstress test, biophysical profile

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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.

Nonreactive result.

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

URL of this page: https://medlineplus.gov/lab-tests/nonstress-test/

A nonstress test is a safe, noninvasive test for pregnant women. Noninvasive means it doesn't cut into the skin or enter any part of the body. The test measures the heart rate of an unborn baby as the baby moves in the uterus. 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 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, or in some cases, delivery may be induced. Inducing labor is when a provider gives you medicine or uses other methods to start labor before it begins naturally.

Other names: fetal nonstress test, NST

A nonstress test is used to check a baby's heart rate before birth. The test is usually done in the third trimester of pregnancy, most often between weeks 38 and 42.

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

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

  • You will lie on a reclining chair or exam table.
  • A health care provider will spread a special gel on the skin over your abdomen.
  • 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.
  • If your baby isn't active or moving during that time period, he or she 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. He or she 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.

You don't need any special preparations for a nonstress test.

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

Nonstress test results are given as one of the following:

  • Reactive or Reassuring. This means the baby's heart rate increased two or more times during the testing period.
  • Nonreactive. This means the 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. The baby may simply 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 delivery induced if it is late enough in your pregnancy.

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

Additional noninvasive tests for an unborn baby's heart rate include:

  • Biophysical profile. This test combines a nonstress test with an ultrasound. An ultrasound is an imaging test that 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 for 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.

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