Non-stress Test (NST): Why It Is Done, Procedure & more

Non-Stress Test During Pregnancy

As a pregnant lady, you will have to undergo a series of tests and appointments to ensure the health of your body and your child. While most of these tests take a small toll on your physical or mental well-being, there is one test which puts no stress on either you or your child. Learn more about it below.

What is a Non-Stress Test?

One of the most common tests associated with high-risk pregnancies, that doctors perform after the 27th week of pregnancy, is the foetal non-stress test or NST. It is called so because it does not trouble your baby while it is being performed; in fact, all it does is observe your baby’s natural activity. It is used to monitor the foetus’ heart beat to gain an understanding of its health status. First, the baby’s heart rate is measured when it’s resting or asleep, and later measured when it is active. If the heart rate matches the activity level, you can be rest assured that the baby is receiving enough nutrients and oxygen. The NST is usually suggested when there is a higher chance of foetal mortality, as this test can tell if you or your foetus require hospitalisation or treatment or in case a pregnancy has gone beyond the suggested due date.

Who Needs to Take This Test?

The NST is very commonly recommended during pregnancy, but especially so for high-risk pregnancies, overdue labour, suboptimal conditions in the uterus, complications in previous pregnancies, and so on. The NST is also suggested if ultrasounds show that the baby is smaller than expected or if the baby’s movements are less than expected. It can also be performed if you have problems like preeclampsia or gestational diabetes.

When is a Non-Stress Test Done?

Pregnancy non-stress test monitoring is suggested in the third trimester, around 4-5 weeks before the due date. This is because the foetus can only provide accurate heart rate measurements after a gestation period of at least 28 weeks.

Why is an NST Performed?

The NST is done to prevent the possibility of foetal hypoxia, that is lack of oxygen supply to the foetus which could have severe complications. In addition to being overdue for labour, there are several other reasons why a nonstress test may be performed.

  • If you have medical conditions like gestational diabetes, heart diseases, blood pressure and hypertension, they can damage the health of the foetus.
  • If you have polyhydramnios (a condition wherein there is excessive amniotic fluid in the amniotic sac surrounding the foetus) or oligohydramnios (lack of sufficient amniotic fluid), pregnancy complications may arise.
  • Late-pregnancy amniocentesis or external cephalic versions (the procedure of turning a baby from breech/transverse to a vertex or head down position) might affect the baby.
  • Reduced growth or movements of the foetus might indicate further issues.
  • Previous miscarriages or stillbirths increase the risks of foetal death.
  • The foetus has a genetic abnormality that requires monitoring.

How Often is a Non-Stress Test Done During Pregnancy?

An increased risk of pregnancy complications might imply getting an NST done at least twice a week, after the 28th week of gestation. The frequency of NSTs performed will depend on the severity of the situation, so make sure you ask your doctor for recommendations. If your doctor suspects the possibility of foetal hypoxia, they might even ask you to take daily non-stress tests.

How Often is a Non-Stress Test Done During Pregnancy?

Procedure for Performing The Non-Stress Test During Pregnancy

The procedure begins with lying on the left side of your body, with your back supported. Two gadgets are attached to your pregnancy bump, one which records uterine contractions and the other records the synchrony between foetal heart rate and movement. Occasionally, the baby might be asleep, so the doctor might suggest you eat or drink something to wake it up. The same result can also be achieved by gently nudging your belly. The test may take up to an hour, so feel free to use the bathroom beforehand. The test is completely painless for both you and the baby.

When Do You Get the Test Results and What Do They Mean?

The results of the test can be obtained immediately after it is performed. There are two main kinds of results for a non-stress test:

1. Reactive

The results are reactive, or normal if the baby’s heart rate increases to at least 15 bpm over the resting heartbeat after moving for 10-15 seconds at least. The baby has to do this twice within a 20-minute cycle for the results to be considered reactive.

2. Nonreactive

If the foetal heart rate does not increase with movement, or if the foetus does not move after at least 60-90 min, the non-stress test interpretation is nonreactive. A non-reactive test result could mean a diagnosis of foetal hypoxia or problems with the placenta. However, it could also not mean anything is wrong, and the doctor might recommend you repeat the NST after a few hours, or take some other tests to confirm the diagnosis.

Is There a Need for Further Testing?

Even though the test is non-reactive, the doctor cannot say if it is due to poor oxygen supply or other reasons such as maternal medications, foetal sleep patterns, or genetic defects. There are two main tests you can take if you have a nonreactive NST:

1. Contraction Stress Test

This test will inform the doctor how stressful labour and delivery is going to be for the baby. The contraction stress tests measure how the foetal heartbeat changes to stress of uterine contractions. The doctor will give you oxytocin, which stimulates uterine contractions, but in a milder way. A reduction in the bpm of the baby during a contraction means that it may find the delivery stressful.

2. Biophysical Profile

This test is a non-stress test in conjunction with ultrasonography. It measures foetal breathing rate, activity, body structure as well as the amniotic fluid in the uterus. An abnormal biophysical profile test implies an early delivery.

Are There Any Risks or Side Effects Linked to The Non-Stress Test?

The NST is non-invasive, which that means it does not involve physical pain or danger. One risk is that the NST might not be able to detect the right complication or indicate the wrong one, causing more tests and procedures to be conducted.

The non-stress test is one of the most important and risk-free tests you can go through to ensure the well-being of your child. Meet with your doctor regularly to keep a tab on the baby’s health. If the NST indicates any dangers, your doctor will most likely recommend an induced delivery.

Also Read: A Guide To Non-Invasive Prenatal Testing (NIPT)

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