In prenatal care, the NST medical abbreviation stands for nonstress test, a painless check that records the baby's heart rate while the pregnant person rests, to see whether the heart rate speeds up in a healthy way.
It is called nonstress because nothing is done to stress the baby, unlike older tests that used contractions. The test is common in the third trimester for pregnancies that need closer watching. Results are usually written as reactive or nonreactive, words that can be confusing at first glance, and this page explains both.
At a glance
Stands for
Nonstress test (also written non stress test)Used in
Prenatal care, often in the third trimesterMeasures
Fetal heart rate and how it changes with movementTypical length
About 20 to 40 minutesResult terms
Reactive (reassuring) or nonreactive (needs more checking)Related test
Biophysical profile (BPP), which adds an ultrasoundSpecialty
Obstetrics and maternal fetal medicine
What the NST medical abbreviation test involves
The pregnant person sits or reclines, often tilted slightly to one side. Two belts hold sensors on the belly: one picks up the baby's heartbeat with ultrasound, and one senses tightening of the uterus. Some units give a button to press each time the baby moves. A machine prints or displays the heart rate as a running line.
A healthy baby's heart rate naturally rises for short bursts when the baby moves. The test looks for these rises, called accelerations. If the baby seems asleep, staff may wait longer or use a gentle sound device to wake the baby.
Reactive versus nonreactive
From about 32 weeks on, a test is usually called reactive when there are at least two accelerations in 20 minutes, each rising about 15 beats per minute above the baseline and lasting about 15 seconds. Before 32 weeks, smaller rises of about 10 beats for 10 seconds are often accepted. Units may use slightly different rules.
| Result | General meaning | Usual next step |
|---|---|---|
| Reactive | Reassuring heart rate pattern | Continue the regular testing plan |
| Nonreactive | Not enough accelerations seen in the time window | Longer monitoring, BPP, or other checks |
A nonreactive result is common and often happens because the baby was sleeping. It means more information is needed, not that something is wrong.
Reading an NST line in a prenatal note
Clinic note: "NST at 36 wks: reactive, baseline FHR 140, moderate variability." At 36 weeks the test was reassuring. FHR means fetal heart rate, which sat around 140 beats per minute, and moderate variability means the normal small wiggles in the line were present.
A normal fetal heart rate baseline is usually about 110 to 160 beats per minute. Notes may also mention decelerations, which are dips in the rate, and whether contractions were seen.
Why NST medical abbreviation pregnancy testing is ordered
An NST is ordered when there is a reason to watch the baby more closely, such as:
- High blood pressure or diabetes in pregnancy, including HTN
- A baby measuring small, sometimes noted as IUGR
- Fewer movements than usual
- Twins or other multiples
- Going past the due date
- Low amniotic fluid or a past pregnancy loss
It is often done once or twice a week in these cases, depending on the care plan.
Before and after the test: what to ask
- Should I eat a snack before the test?
- How often will I need this test, and for how long?
- What would happen if the result is nonreactive?
- What changes in the baby's movements should I report right away?
These notes describe the test in general terms. Your obstetric clinician or midwife can go over your own tracing and plan with you.
Frequently asked questions
What does NST mean in pregnancy?
NST means nonstress test. It records the baby's heart rate for about 20 to 40 minutes to see whether it speeds up with movement.
What does a reactive NST mean?
A reactive result means the baby's heart rate rose enough times during the test, which is reassuring. The usual care plan continues.
Is a nonreactive NST bad?
Not necessarily. It often happens when the baby is asleep. It means more monitoring or another test, such as a biophysical profile, is needed.
Does a nonstress test hurt?
No. It uses belts with sensors on the belly and does not involve needles or contractions.