In a third‑trimester pregnancy with a non‑reactive non‑stress test (NST), how should the test be verified and what is the subsequent management—including repeat testing, biophysical profile (BPP), Doppler studies, and timing of delivery—based on gestational age?

Management of Non-Reactive NST in Third Trimester

A non-reactive NST requires immediate further evaluation with either a full biophysical profile (BPP) or modified biophysical profile (NST + amniotic fluid assessment) to determine if delivery is indicated—never use a non-reactive NST alone for delivery decisions. 1

Initial Verification and Extended Testing

When confronted with a non-reactive NST, the test should be extended and supplemented:

• Extend the monitoring period to ensure adequate observation time, as the NST is defined as reactive when ≥2 fetal heart rate accelerations of 15 bpm lasting 15 seconds occur within 20 minutes 1
• Proceed immediately to modified BPP or full BPP after confirming non-reactivity, as this provides both acute (NST) and chronic (amniotic fluid) markers of fetal well-being 1
• The ultrasound component continues until all four components meet criteria or 30 minutes have elapsed, whichever comes first 1

Subsequent Management Algorithm

The management pathway depends critically on BPP scoring and gestational age:

If BPP Score is 8-10 (Reassuring):

• Continue surveillance with increased frequency (twice weekly) for preterm pregnancies 1
• This score has exceptional reassurance value, with perinatal mortality of only 1.0 per 1,000 and false-negative rate of 0.7 per 1,000 within one week 1
• Weekly or twice-weekly testing has become standard clinical practice in high-risk pregnancies 1

If BPP Score is ≤6 (Non-Reassuring):

• Deliver immediately, regardless of gestational age 1
• This represents significant fetal compromise requiring urgent intervention 1

If Oligohydramnios is Detected:

• Deliver at term (≥37 weeks), as oligohydramnios is an independent risk factor for stillbirth 1
• Amniotic fluid assessment is critical—a maximum vertical pocket (MVP) ≥2 cm is considered normal throughout gestation 1

Role of Doppler Studies

Umbilical artery Doppler should be incorporated when specific conditions are present:

• Perform Doppler if fetal growth restriction is suspected, as this has demonstrated a 29% reduction in perinatal deaths (from 1.7% to 1.2%) 1
• Absent or reversed end-diastolic flow is always abnormal and requires urgent management 1
• Deliver at ≥34 weeks after corticosteroids for absent end-diastolic flow, and at ≥32 weeks for reversed end-diastolic flow 1
• Doppler is reserved exclusively for high-risk pregnancies with suspected intrauterine growth restriction—routine use in low-risk populations provides no benefit 1

Timing of Delivery Based on Gestational Age

At Term (≥37 weeks):

• Abnormal antenatal test results, including non-reactive NST with abnormal BPP, are an indication for delivery 1
• Oligohydramnios detected at term warrants delivery 1

Preterm (<37 weeks):

• Management depends on BPP score and presence of growth restriction 1
• If growth restriction with abnormal Doppler: deliver at 32-34 weeks depending on severity of Doppler findings 1
• Daily or more frequent testing may be indicated in critical situations such as growth restriction or abnormal Doppler findings 1

Critical Caveats

• No antenatal test can predict stillbirth related to acute events such as placental abruption or cord accidents, regardless of test frequency 1, 2
• A reactive NST has a negative predictive value >99.9%, with stillbirth risk within 1 week of only 0.8 per 1,000 cases (0.08%) 1
• The non-reactive NST is more specific than sensitive, making it a better indicator of fetal health than fetal illness when reactive 3
• Never ignore amniotic fluid assessment, as oligohydramnios is an independent risk factor for stillbirth 1
• False negatives, though uncommon, have been associated with cord accidents and abruption in historical series 2