Gestational age assessment and preterm classification — OSCE

Objectives

1. Explain in plain language how gestational age is assigned antenatally and confirmed postnatally. [3] [1]
2. Explain what the very-preterm and low-birthweight labels mean and why they are not the same thing. [2]
3. Describe the care and screening that the classification triggers. [4] [5]
4. Outline the corrected-age follow-up plan and invite the family into shared understanding. [5]

Candidate brief

12-minute station. The parents are at the bedside of their 31-week infant, weighing 1500 g, on day 2. The infant is on continuous positive airway pressure and feeds are being established as expressed milk. The parents ask: "How do you know our baby is 31 weeks? What does very preterm mean? Is 1500 g dangerous? What happens next and for how long?" They are anxious but engaged. [3]

Expected actions

• Acknowledge the parents' anxiety and use plain language throughout. [3]
• Explain dating: a first-trimester ultrasound measured the baby from crown to rump, which is the most accurate way to time a pregnancy, within about a week. [3]
• Explain that a bedside maturity check (the New Ballard Score) confirms the age from the baby's muscle tone and skin, ear and other signs. [1]
• Separate the two labels clearly: very preterm means born early, a measure of time; 1500 g means very low birthweight, a measure of size; the baby is also appropriate for gestational age, meaning the size matches the age. [2]
• Outline what the classification triggers: care in the special-care or intensive nursery, cranial ultrasound checks, eye examinations for retinopathy, feeding support, and growth plotting on special charts. [4] [5]
• Describe corrected-age follow-up: milestones are assessed allowing for the weeks born early, continuing to about 2 years, with structured reviews to school age. [5]

Examiner prompts

• "How do you know our baby is exactly 31 weeks?" — Explain first-trimester crown-rump-length ultrasound accuracy and confirmatory postnatal scoring. [3] [1]
• "Is 1500 g a dangerous weight?" — Reframe size as relative to gestational age; this baby is appropriate for gestational age, so the weight matches the age. [2]
• "Will our baby catch up?" — Explain corrected age, Fenton to WHO transition, and structured follow-up; offer honest, hopeful, probabilistic language. [5]

Marking foci

• Clear, plain-language separation of gestational age from birthweight from size-for-gestational-age [2]
• Accurate description of dating and postnatal confirmation [3] [1]
• Correct description of the screening and care the classification triggers [4] [5]
• Honest, hopeful counselling and corrected-age follow-up framing [5]