What Is Non-Stress Test (NST) And How To Interpret It

Non Stress Test

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You have to undergo a litany of tests during pregnancy. There are tests 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 from time to time. 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 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. Also, the doctor will not use any medications to make the baby move but records the natural movements (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?

A nonstress test (NST) checks the fetal heart rate to tell you about the oxygen supply to the baby. It tells you if your baby is healthy and getting enough oxygen.

Like an adult’s heart, the fetus’ heart, too, should beat faster when active. If it is not, the NST will detect the abnormality, paving the way for further testing, monitoring, and treatment to prevent any complications.

Your doctor would suggest the nonstress test if:

  • Yours is a high-risk pregnancy due to 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.
  • You have Rh-negative blood (1).

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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How Should You Prepare For A Nonstress Test?

No preparation is needed for the NST. However, there are some things you can do to make your baby active.

  • Consume a healthy snack half-an-hour to one hour before the test. Follow the regular diet and try to schedule the NST right after the snack or meal time.
  • Do not smoke before the test, if you have not been able to stop smoking during pregnancy. Nicotine will make the baby less active.
  • If you are on medications other than iron and vitamin supplements, let your doctor know as certain medications can affect the results of the test.
  • Your baby may have irregular sleep cycles. If the baby is not active during the NST, the doctor will find different ways to stimulate the baby: changing your position, touching your abdomen or using the acoustic device (a sound device that makes vibrations) to awaken the baby (2).

Most importantly, avoid anxiety and be relaxed; and this is possible if you understand the procedure of the test.

[ Read: Fetal Heart Monitors ]

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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.
  • Before the test begins, your doctor checks your blood pressure. She might note the blood pressure at regular intervals during the test.
  • 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. Let’s know what the results could have for you.

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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 indicates your baby is doing fine. 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: It means that the result is not conclusive, and there is a 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 delivery if you are almost nearing your full-term. 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. Contraction stress test: This test helps read the baby’s heart rate during the uterine contractions. It helps assess how the baby might do during labor.

Labor is stressful for the baby. With every contraction, the baby receives lesser oxygen and blood. While that is not really a problem, some babies can face difficulty during this period. A CST will, therefore, show how the baby reacts to the stress of a contraction and prepare for any possible complications.

This test involves intravenous administering of oxytocin (Pitocin), which will stimulate the contractions in the uterus. You will experience similar, but milder, contractions as you would in labor. If the baby’s heart rate is slower rather than faster after each contraction, it is an indication that the baby will have difficulty during labor.

When the results are abnormal, you may have to go for early delivery (5).

  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 (6).

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

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Frequently Asked Questions

1. What is the CPT code for NST?

The CPT code for NST is 59025. CPT (Current procedural terminology) is a medical code which is set to delineate therapeutic, diagnostic and surgical services and procedures for processing claims, conducting research, developing medical guidelines and other forms of healthcare documentation. It is developed by the American Medical Association (AMA) (7).

2. What is the difference between NST and CTG during pregnancy?

An NST uses a cardiotocogram (CTG), which monitors the fetal heart rate and uterine contractions using electronic devices, for assessing fetal health condition. A CTG is a recording of the nonstress test.

3. Why does NST measure contractions, and why will you have them?

Firstly, you may or may not have contractions around this time. Even if you do, they could be Braxton Hicks contractions that are irregular, mild or sporadic. They are harmless and common during the third trimester. But, if you have not entered the 37th week of pregnancy and are experiencing continuous, recurring contractions, it could be a sign of preterm labor (8). Then, your doctor will check if your cervix is dilated.

Secondly, it helps you know if there is any change in the fetal heart rate based on the contractions. If the heart rate decreases during a contraction, it is the sign of a placental problem (9).

[ Read: When Is NIPT Done ]

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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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Rebecca Malachi

She is a Biotechnologist with a proficiency in areas of genetics, immunology, microbiology, bio-engineering, chemical engineering, medicine, pharmaceuticals to name a few. Her expertise in these fields has greatly assisted her in writing medical and life science articles. With 8+ years of work experience in writing for health and wellness, she is now a full-time contributor for Momjunction.com. She is passionate about giving research-based information to readers in need. Apart from writing, she is a foodie, loves travel, fond of gospel music and enjoys observing nature in silence. Know more about her at: linkedin.com/in/kothapalli-rebecca-35881628
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