What is the significance of a biophysical profile (BPP) score in a patient with severe fetal growth restriction (FGR) and what are the implications for delivery?

Biophysical Profile Score in Severe Fetal Growth Restriction

Direct Answer

In severe fetal growth restriction (FGR), a BPP score of 8-10 indicates current fetal well-being with >99% certainty that the fetal pH is >7.25, while a score ≤6 mandates immediate delivery regardless of gestational age due to high risk of fetal acidemia and stillbirth. 1

Understanding BPP Score Significance

The BPP correlates over 90% with current fetal pH from the second trimester onward, making it the gold standard for assessing immediate fetal acid-base status in FGR 2. Each component (fetal breathing, movement, tone, and amniotic fluid) receives 0 or 2 points for a maximum score of 8, or 10 if the nonstress test is included 1.

Score Interpretation in Severe FGR:

• Score 8-10: Indicates a well-compensated fetus with pH >7.25 and very low risk (<0.8 per 1,000) of fetal death within one week 1, 2
• Score 6: Equivocal result requiring repeat testing within 12-24 hours and consideration of delivery at term 1
• Score ≤4: Indicates probable fetal acidemia requiring immediate delivery 1

Critical Limitation: BPP Cannot Predict Future Deterioration

The BPP only reflects current fetal status and cannot predict future well-being or acute catastrophic events like placental abruption or cord accidents. 1, 3 This is why Doppler velocimetry and amniotic fluid assessment are essential for determining surveillance frequency 2.

Integration with Doppler for Delivery Timing

In severe FGR, Doppler changes precede BPP deterioration by a median of 4 days, making umbilical artery Doppler the primary tool for anticipating deterioration 4. The sequence of deterioration typically follows this pattern:

1. First: Umbilical artery Doppler worsens (elevated pulsatility index, then absent/reversed end-diastolic flow) 4
2. 2-3 days later: Fetal breathing movements decline 4
3. Next day: Amniotic fluid volume drops 4
4. Day of delivery: BPP score drops abruptly with loss of movement and tone 4

Delivery Thresholds Based on Combined Assessment:

• Absent end-diastolic flow + normal BPP: Deliver at 34 weeks after corticosteroids 5
• Reversed end-diastolic flow + normal BPP: Deliver at 30-32 weeks with intensive monitoring 5
• Any BPP score ≤6: Deliver immediately regardless of Doppler findings or gestational age 1
• Normal Doppler + BPP 8-10: Continue surveillance; can proceed to 37-38 weeks depending on severity 5

Surveillance Frequency in Severe FGR

Between 30-70% of growth-restricted fetuses with nonreactive nonstress tests require BPP scoring to verify well-being, and 8-27% will have abnormal scores necessitating delivery that Doppler alone would not detect. 2

• Normal umbilical artery Doppler: Weekly BPP and Doppler 5
• Elevated pulsatility index but present diastolic flow: Twice weekly BPP 1, 5
• Absent end-diastolic flow: Daily BPP with 2-3 times weekly Doppler 5
• Reversed end-diastolic flow: Hospitalization with BPP 1-2 times daily 5

Common Pitfalls to Avoid

Do not rely on BPP alone for delivery decisions in severe FGR. 1, 2 The BPP must be integrated with:

• Umbilical artery Doppler (the only Doppler with Level I evidence for improved outcomes) 5
• Amniotic fluid volume (reflects chronic placental insufficiency over the preceding week) 1
• Gestational age and neonatal viability considerations 1, 6

Do not assume a normal BPP guarantees safety for more than one week. 1, 3 In severe FGR with abnormal Doppler, deterioration can be rapid and testing frequency must be intensified 4, 2.

Do not delay delivery beyond recommended gestational ages based on a reassuring BPP if Doppler shows absent or reversed end-diastolic flow. 5 Studies show integrated surveillance combining frequent heart rate monitoring with BPP and Doppler achieves stillbirth rates of 0-4% versus 8-11% with empiric surveillance 2.

When BPP May Be Falsely Reassuring

A case report demonstrates that despite a BPP score of 8/8 with active tone, movements, breathing, and normal fluid, a severely compromised fetus with massive intracranial hemorrhage was delivered acidotic 7. This underscores that no antenatal test, including BPP, can predict acute catastrophic events. 1, 3