Biophysical Profile

The biophysical profile combines a cardiotocographic assessment with ultrasound observation of foetal behaviour and amniotic fluid volume over 30 minutes. Five variables are scored 0 or 2: foetal heart rate reactivity, foetal breathing movements, gross body movements, foetal tone, and amniotic fluid volume.

Acute hypoxia affects the behavioural variables in a predictable order as the central nervous system adapts. Heart rate reactivity and breathing movements are lost first, followed by gross movements and tone. Amniotic fluid volume reflects chronic placental function.

Modified profile. A non-stress test combined with an amniotic fluid index (or deepest vertical pocket) is used as a quicker, less resource intensive screen.

Indications. Reduced foetal movements, foetal growth restriction, hypertensive disorders, diabetes, post-term pregnancy, a non-reactive non-stress test, and oligohydramnios or polyhydramnios.

Preparation and technique. The profile is performed from about 28 weeks. The observation period is 30 minutes, ended early when criteria are met. The mother is semi-recumbent.

Criteria for a score of 2.

• Foetal breathing movements: at least one episode of rhythmic breathing lasting at least 30 seconds.
• Gross body movements: at least 3 discrete movements of the body or limbs.
• Foetal tone: at least one episode of extension with return to flexion, or opening and closing of the hand.
• Reactive heart rate: at least 2 accelerations of 15 beats/min lasting at least 15 seconds.
• Amniotic fluid: at least one pocket measuring 2 cm in the vertical dimension (an amniotic fluid index of 5 cm or more is also used).

Contraindications and precautions. None specific. Scores are interpreted with caution before 28 weeks.

Interpretation.

• 8 to 10 is reassuring, with normal amniotic fluid.
• 6 is equivocal and is repeated within 24 hours, or delivery is considered at term.
• 4 or less is abnormal and requires urgent review, and delivery is considered depending on gestation and the clinical picture.
• A score of 8 with oligohydramnios is treated as abnormal, because reduced fluid suggests chronic compromise.

Causes of a low score. Foetal hypoxia from placental insufficiency, foetal sleep, maternal sedatives, congenital anomaly, infection, and foetal growth restriction.

Critical values and findings needing immediate action.

• A score of 4 or under requires same day specialist review and consideration of delivery.
• A score of 0 to 2 indicates severe compromise and requires immediate action.

Limitations and artefacts. Foetal sleep can lower the score. Operator experience affects accuracy. The profile detects acute hypoxia and does not measure growth.

Follow up tests. Umbilical artery Doppler, middle cerebral artery Doppler, growth ultrasound, and repeat profile.

Special groups. Preterm pregnancies below 32 weeks need lower thresholds for behaviours. Multiple pregnancy requires assessment of each fetus.