Non-Stress Test (NST)
A non-stress test (NST) monitors your baby's heart rate to assess wellbeing. It's called "non-stress" because no stress is placed on the baby — it simply observes how the heart responds to movement.
Typically performed: Third trimester, usually from week 28 onwards
How It's Done
Two monitors are placed on your abdomen with elastic bands: one to record the baby's heart rate, one to detect uterine contractions. You sit or lie comfortably for 20–40 minutes. You may be given a button to press when you feel baby move. A snack before the test can encourage baby activity.
Reactive vs. Non-Reactive Results
A reactive (normal) NST shows two or more accelerations of the fetal heart rate by at least 15 beats per minute for at least 15 seconds within a 20-minute period. A non-reactive result means these accelerations weren't seen — but this doesn't necessarily mean something is wrong. Baby may simply have been asleep, and the test may be extended or a biophysical profile ordered.
Why It's Ordered
NSTs are routinely ordered for high-risk pregnancies and when the due date has passed. Reasons include gestational diabetes, hypertension, decreased fetal movement, post-term pregnancy, intrauterine growth restriction (IUGR), and previous stillbirth.
Frequently Asked Questions
No — it's completely painless. The monitors are held in place by stretchy belts on your abdomen.
This varies by indication. High-risk pregnancies may have weekly or twice-weekly NSTs from 28–32 weeks onwards. Postterm pregnancies (beyond 41 weeks) typically require twice-weekly NSTs.
The test is usually extended to 40–60 minutes, or a biophysical profile (BPP) is done to get a broader picture of fetal wellbeing. A non-reactive NST rarely leads directly to delivery without further assessment.