Biophysical Profile
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Direct answer
The biophysical profile (BPP) is a composite antenatal test of fetal wellbeing combining the non-stress test with four ultrasound variables — breathing, movements, tone and amniotic fluid volume — each scored 2 or 0 for a maximum of 10. It estimates the probability of chronic hypoxaemia, because the variables disappear in a predictable sequence as oxygenation fails, while amniotic fluid reflects the longer-term picture. A score of 8-10 is reassuring, 6 is equivocal and repeated within 24 hours (or delivery when mature or with oligohydramnios), and 4 or less generally mandates delivery at a viable gestation.
What you must remember
- Components and thresholds: fetal breathing — at least one 30-second episode in 30 minutes; gross body movements — at least three; fetal tone — at least one extension-flexion episode; amniotic fluid volume — a deepest vertical pocket of 2 cm or more; plus the reactive non-stress test.
- Scoring: each variable scores 2 (normal) or 0 (absent or abnormal); 8-10 normal, 6 equivocal, 4 or less abnormal; the ultrasound part usually takes under 30 minutes when the fetus is well.
- Physiological gradient: with progressive hypoxaemia the variables are lost in reverse order of fetal appearance — reactivity first, then breathing, movements and finally tone; tone loss marks the pre-terminal state.
- Interpretation and action: 8-10 — repeat per risk protocol; 6 — repeat in 24 hours, delivering if mature, growth-restricted with abnormal Doppler or oligohydramniotic; 4 or less — deliver if viable.
- Oligohydramnios carries special weight at any score: it reflects chronic hypoxaemia with reduced fetal urine output, and with maturity or growth restriction it tips management toward delivery.
- Uses: second-line after a non-reactive non-stress test and for surveillance in growth restriction, post-term pregnancy, diabetes and hypertensive disease; correlates inversely with cord blood pH and perinatal mortality.
- Practical limits: false-positives occur with fetal sleep, maternal sedation, steroids, hyperglycaemia and smoking — interpret alongside gestation, Doppler and context.
Common confusion
The BPP is treated as pass-fail, when its strength is gradation and the score-specific action ladder — a score of 6 is equivocal, not abnormal, and is repeated within 24 hours unless oligohydramnios, maturity or abnormal Doppler force delivery. Only amniotic fluid reflects chronic status; the other four respond to acute states such as fetal sleep or maternal sedation, which is why a low score is repeated rather than reflexively operated.
Exam-focused takeaway
Stems quote component performance and ask for the score or next step — the 24-hour repeat for a score of 6 and delivery for 4 or less are the tested actions. Numeric thresholds (30-second breathing, three movements, one tone episode, 2 cm pocket) and the order of variable loss recur as one-liners.
Frequently asked questions
What are the five components of the biophysical profile?
Non-stress reactivity, fetal breathing, gross body movements, fetal tone and amniotic fluid volume — each scored 2 or 0, maximum 10.
What thresholds define each ultrasound variable?
Breathing of 30 seconds in 30 minutes, three or more body movements, one or more extension-flexion tone episode, and a deepest vertical fluid pocket of 2 cm or more.
What does a score of 6 mean?
An equivocal result — repeat the profile within 24 hours, unless oligohydramnios, lung maturity or abnormal Doppler with growth restriction indicates delivery.
Why does amniotic fluid carry special weight?
Because it alone reflects chronic hypoxaemia — blood is redistributed away from the fetal kidneys, urine output falls and the pocket shrinks even when acute variables look acceptable.
In what order are variables lost with fetal hypoxia?
Reactivity, then breathing, then movements, then tone — tone loss indicates pre-terminal compromise.