Non-Stress Test (NST) During Pregnancy: Procedure And Result Interpretation

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There are many tests during pregnancy to confirm your well-being and the baby’s too. If your pregnancy has some complications or you have certain health issues, then the doctor would suggest some additional tests such as the nonstress test.

The prenatal nonstress test monitors the baby’s heartbeat for a period of time as well as contractions. In this post, MomJunction tells you what the test is, why it is necessary, and how it is done.

What Is A Nonstress Test?

A nonstress test, also known as fetal heart rate monitoring, is a simple and non-invasive test performed typically after 28 weeks of pregnancy. It measures the heart rate of the fetus in response to its movements.

The nonstress test is called so because it does not pose any physical stress to you or your fetus (1).

The test may be a simple one, but it is important to track the health of the baby.

[ Read: What Is A Contraction Stress Test ]

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Why Would You Need A Nonstress Test?

There are many indications to perform a nonstress test and typically some complication related to pregnancy may warrant the performance of NSTs.

Some reasons why your doctor would recommend the nonstress test are:

  • kidney, thyroid or heart disease, high blood pressure or diabetes.
  • Your baby’s growth is slow, he or she moves less than usual.
  • Your amniotic fluid levels are either too high or too low.
  • You had undergone procedures such as external cephalic version or third-trimester amniocentesis.
  • You have passed your due date.
  • Your baby is diagnosed with any birth defect or abnormality.
  • You previously had a miscarriage or stillborn baby.
  • You are carrying twins or multiples.

Your doctor might recommend the NST once or twice a week at first, and occasionally later, depending on your and your baby’s condition.

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[ Read: Fetal Heart Monitors ]

How Is The Nonstress Test Done?

The test is usually performed in a hospital and involves the below procedure.

  • Once you lie down on your back, your abdomen is secured with two belts with attached monitors.
  • One belt measures the heart rate of your baby while the other measures any uterine contractions you may have.
  • You can notice your baby’s movements, which are recorded on the monitor and printed out at the end of the test.
  • The graphs on the paper help the doctor assess your baby’s heartbeats during the movements.
  • The test lasts for about 20 minutes. If the baby is asleep or inactive, it may be extended by another 20 minutes. Your doctor will try stimulating the baby using an acoustic device that makes a noise and awakens the baby. You may also be told to eat or drink something to make the baby active (3).

Once the test is done, the results are available almost immediately.

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What Should You Know About The Nonstress Test Results?

The doctor would use two key phrases to interpret the results:

  1. Reactive (normal): A normal result, If the fetal heart beats faster (around 15 beats per minute) during a movement of at least 15 seconds, on two separate accelerations in a 20-minute period, the result is reactive (4).
  1. Non-reactive: There usually is need for further testing. The result is non-reactive when it does not match the criteria mentioned in the first point. While the result is worrisome, a non-reactive result could also be because your baby was asleep or inactive during the process (3).

If the test extends to 40 minutes and the results are non-reactive, the doctor may recommend a follow up ultrasound or even delivery if you are at your due date. If you are not close to completing the full-term, your doctor will conduct some other prenatal tests to assess your baby’s health. The follow-up tests include contraction stress test (CST), biophysical profile (BPP) and modified biophysical profile (MBPP).

[ Read: Fetal Echocardiography Procedure ]

Follow-up tests:

  1. Biophysical profile: This test combines the NST with a fetal ultrasound. It assesses the baby’s breathing, movements, muscle tone and amniotic levels. The test results can be normal, abnormal or sometimes unclear. If heartbeat results are abnormal, you should go for early delivery, and if the results are unclear, you will have a retest.
  1. Modified biophysical profile: MBPP is also an NST along with an ultrasound that only looks for the amniotic fluid levels. This test is enough to determine the baby’s health and takes lesser time than a BPP (1).

Read on to know about the commonly used terms in NST results.

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[ Read: When Is NIPT Done ]

The ultimate goal of this test is to reassure you and your partner that the baby is doing well. It does not have any adverse effect on you or the baby but helps the doctor detect any abnormalities in oxygen supply. You may talk to your doctor before the test to allay any fears.

If you have already had the test during pregnancy, share your experiences in the comments section below.

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