When Do Nonstress Tests and Biophysical Profiles Start?

What does the evidence say about when nonstress tests and biophysical profiles start during pregnancy?

1. Antenatal fetal surveillance is generally considered around 32 weeks for many high-risk pregnancies because earlier testing has more false nonreactive results. The precise start should reflect the condition, severity, expected deterioration, and gestational age at which an abnormal result would change care. 1
2. A reactive NST at 32 weeks or later requires at least two fetal-heart-rate accelerations of 15 beats per minute for 15 seconds within 20 minutes. Before 32 weeks, a 10-by-10 criterion is used. A nonreactive result may reflect fetal sleep or compromise and can prompt further assessment. 2
3. A full BPP combines an NST with ultrasound assessment of fetal breathing, movement, tone, and amniotic fluid. Each component receives 0 or 2 points for a total of 10. This is different from a growth scan, which estimates fetal size and growth pattern. 1
4. Common reasons to consider surveillance include fetal growth restriction, decreased fetal movement, hypertensive disorders, pregestational or medication-managed gestational diabetes, kidney disease, lupus or antiphospholipid syndrome, multiple gestation, and a pregnancy continuing beyond the due date. Indication alone does not set one universal schedule. 3
5. ACOG characterizes its outpatient surveillance tables as guidance on indications, timing, and frequency, not proof that surveillance improves outcomes for every listed condition. Decisions should be individualized and shared because the evidence base varies by risk factor. 4

Is when nonstress tests and biophysical profiles start safe in each trimester?

• First trimester. NSTs and BPPs are not routine first-trimester screening tests. If a serious maternal condition is already known, the care team can outline which later surveillance method is relevant and when its results could change care.
• Second trimester. Before 32 weeks, a normal fetus is more likely to have an immature, nonreactive NST pattern. Earlier surveillance may still be selected for severe disease, but results require gestational-age-aware interpretation and a plan for what action would follow.
• Third trimester. Around 32 weeks is a common starting point for many continuing high-risk conditions. Stable cases may be checked weekly, while rapidly changing conditions may prompt twice-weekly or individualized testing; the optimal schedule is not established for every indication.