Fetal Non-Stress Test During Pregnancy: Procedure, Risks and Results


A Foetal Non-Stress Test (NST) is a prenatal test for checking on your baby’s health. It monitors the fetal heart rate to check its response to the fetal movements. Here’s all you need to know about it.

In this article:

How is an NST Performed?
Coding NST
Why would an NST be Performed?
Risks and Side Effects on the Mother and the Baby
When is it Performed?
Things to Look for in an NST
What do the Results Mean?

A Guide for Fetal Non-Stress Test During Pregnancy

How is an NST Performed?

During the Fetal Non-Stress Test, your blood pressure will be recorded at regular intervals. The health provider will set a sensor around your abdomen for measuring the fetal heart rate. Another belt is placed for measuring contractions.

The ultrasound probe transmits your baby’s heart rate in bpm or beats per minute that the testing machine records with the help of a non-stress testing strip or grid. Every small vertical grid represents 10 beats. Every small horizontal grid represents 10 seconds and every large horizontal grid implies one minute. The pressure transducer transmits the pressure in mm Hg which has been generated by uterine contractions. Every small vertical grid implies 5 mm Hg.

fetal non stress test cpt code

The test typically lasts for 20-30 minutes to measure the reactivity of the fetal heart rate to the fetal movements. If no movements are recorded, it doesn’t necessarily hint at a problem as your baby might be asleep. In that case, a nurse might wake your baby for the remaining test placing a small buzzer on your abdomen.

Coding NST

NST coders must know what is and aren’t included in the method of the test. Health providers should also meet clinical documentation needs. CMS bundles the Foetal Non-Stress Test with fetal ultrasound codes: 76815, 76818, 76819. CMS also bundles with CPT code 59025, the catheterization codes of 51701 and 51702. Foetal Non-Stress Test service does not have any global days attached. This is good news with respect to the requirement of the coders to report an NST on consecutive days.

The Foetal Non-Stress Test CPT code 59025 can be billed as a global service as a technical component only (modifier -TC) or as interpretation solely (modifier -26). Another uncommon coding guideline for an NST is for multiple fetuses or gestations. The health provider records the fetus and separately documents and interprets the process for every fetal tracing and record.

Why would an NST be Performed?

A Fetal Non-Stress Test is performed for evaluating a baby’s pre-birth health. Its objective is providing necessary information about the baby’s oxygen supply by checking the response of his/her heart rate to his/her movement.

A baby’s heart usually beats faster in later pregnancy when he/she is active. But this response may be disrupted by problems like fetal hypoxia when your baby wouldn’t receive enough oxygen.

The health provider would recommend a non-stress test for the fetus if you have:

  • Multiple pregnancies with specific complications
  • An underlying medical problem like high blood pressure, heart disorder or type 1 diabetes during pregnancy
  • A pregnancy which has extended 14 days past the due date, i.e., post-term pregnancy
  • A history of complications (if any) in your previous pregnancy
  • Possible fetal growth issues or a baby who has reduced fetal movements
  • Rhesus (Rh) sensitization, i.e., a potentially critical state which may typically happen during your subsequent or second pregnancy when the baby has an Rh-positive red cell antigen blood group and you have an Rh-negative blood group.
  • Oligohydramnios or low amniotic fluid

The NST can detect if your baby is not getting sufficient oxygen due to problems related to your placenta or umbilical cord, or other kinds of fetal distress.

The tests might be taken once or twice weekly (or rarely, daily) according to your and the baby’s health.

Risks and Side Effects on the Mother and the Baby

A Foetal Non-Stress Test is a non-invasive procedure that would pose no physical risks or side effects to you or the baby. The term “non-stress” implies that no such activities are done which would impose stress on your baby during the test.

Although the NST can provide you with reassurance regarding the baby’s health, it may also cause anxiety. This is because the test may indicate that there is a problem when no such issue exists. This can result in further testing. However, reassuring tests also cannot predict the future.

Apart from these, remember that while this test is often suggested when you have a higher risk of pregnancy loss, it is not always certain if the test can be beneficial.

When is it Performed?

An NST is usually done after 28 weeks of gestation as your fetus is not adequately developed to respond to the test protocol before this period.

Things to Look for in an NST

The primary objective of the non-stress test for the fetus is to measure the fetal heart rate in response to fetal movements.

Healthy babies show a higher heart rate while they move and their heart rate falls when they are at rest. The concept behind an NST is that sufficient oxygen is needed for the fetal heart rate and activity to be within normal ranges.

At low oxygen levels, your fetus might not respond normally. This is often caused due to issues with your umbilical cord or placenta.

What do the Results Mean?

Results of NST are considered:


Before the 32nd week of pregnancy, results would be considered reactive (normal) if the fetal heartbeat increases to a specific level twice or more above its baseline for a minimum of 10 seconds each within a window of 20 minutes. At the 32nd week of pregnancy or later, if the fetal heartbeat increases to a specific level twice or more above its baseline for a minimum of 15 seconds each within a window of 20 minutes, the results would be regarded as reactive.


If the fetal heartbeat does not meet the criteria discussed above, the results would be considered nonreactive. Nonreactive results may take place if the baby was asleep or inactive during the NST.


You can safely go for a Foetal Non-Stress Test as it is non-invasive and wouldn’t harm you or your baby.

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