NST (Non-Stress Test): How Is the Baby's Heartbeat Monitored in Pregnancy and What Does the Result Mean?

An NST (non-stress test) is a monitoring test, applied over the abdomen, that records how the baby's heartbeat changes with movements in pregnancy. The result is reported as "reactive" or "non-reactive". A non-reactive result does not on its own mean there is a problem; the baby may be asleep at the time, and the doctor generally requests additional monitoring. An NST is not done routinely in every pregnancy but in situations where the doctor thinks it necessary. When the test will start, how often it will be repeated and how long it will last are determined according to the person; the doctor who follows you or the institution performing the test will tell you these details.

What does an NST record, and why is it done?

An NST records the baby's heartbeat while the baby is moving or the uterus is contracting. The heartbeat of a healthy baby speeds up with movement; seeing this change on the recording is reassuring information about the baby's state at that moment. The test has no known risk.

The aim of antenatal fetal monitoring is defined as reducing the risk of stillbirth.

Is an NST done routinely in every pregnancy?

According to research done, there is no clear evidence that recordings of the baby's heartbeat during pregnancy, including NST, improve perinatal outcomes (those around the time of birth); the studies examined were done in high-risk pregnant women, were few in number and were found to be of low quality. For this reason, whether the test will be done is assessed by your doctor according to the person and the state of the pregnancy.

For whom can an NST be recommended?

The test can be recommended in situations such as the following:

• The baby moving less than usual
• The pregnancy going beyond the expected time
• Health problems such as high blood pressure, diabetes, heart disease or a clotting disorder
• A complication in an earlier pregnancy
• Rh incompatibility
• Multiple pregnancy

This list is not closed. Whether the test is necessary for you is decided by the doctor who knows your state of health; a situation appearing in the list does not mean the test will be done, just as a situation not in the list does not rule out the test.

What happens during an NST?

The test is generally done in a semi-reclining or lying position. Two bands are placed on your abdomen: one records the baby's heartbeat and the other the uterine contractions. When you feel the baby move, you press a button you are given; in this way the movement and the change in heartbeat can be assessed together. The health professional performing the test will tell you how long the recording will last.

Is preparation needed before an NST?

Generally no special preparation is needed. Even so, if you have been given an instruction about eating or taking medicines before the test, follow it. Tell your doctor about the medicines you use regularly; some medicines can affect the result.

What do reactive and non-reactive results mean?

A reactive result shows that the baby's heartbeat speeds up with movement as expected and is reassuring. A non-reactive result means that enough speeding up of the heartbeat was not seen during the recording or that the baby moved little. This may not show that there is a health problem: the baby may be asleep or some medicines may have affected the heartbeat. Instead of assessing the result by looking at comments on the internet, go over it with your doctor.

What can be done after a non-reactive result?

After a non-reactive recording, your doctor may request an additional test or monitoring; methods such as ultrasound can be used as an additional assessment. If the pregnancy is sufficiently advanced, monitoring or treatment may be needed. Your doctor determines the next step by assessing the recording and your state of health together.

What are the limits of an NST result?

An NST is a recording of the heartbeat at a particular moment. A reactive result is not an assurance against situations that may arise in the following days. A single test result does not tell the whole picture; the doctor interprets the result together with your baby's movements and your state of health. Even if your test result is good, if you later notice a change in the baby's movements, do not brush it aside by saying "my result was normal".

If the baby's movements change, should you wait for your NST appointment?

When you notice a decrease or change in your baby's movements, you need to seek care from a health professional without delay. There is no particular "normal" number of movements. Having an NST appointment ahead of you is not a reason to postpone seeking care. In late pregnancy, on these visits the baby's heartbeat is monitored and, if necessary, an ultrasound is done; these checks most often end with a reassuring result.

What can you ask your doctor before the test?

• Ask why this test is recommended for you and whether it will be repeated during pregnancy.
• Find out whether the medicines you use could affect the recording result.
• Ask whether there is any instruction for the test day about eating or anything else.
• Find out what the next step will be if it comes out non-reactive and how the result will be communicated to you.
• Ask where and by what route to seek care if there is a change in the baby's movements.