Amniotic fluid disorders — structured oral station (12 minutes)

Opening prompt — "Take the oligohydramnios case first. What is your threshold, and what is your first move?"

Model response — say it in this order: ^[2][5]

• "Oligohydramnios is a deepest vertical pocket under 2 cm or an amniotic fluid index under 5 cm. This woman meets both, so the diagnosis stands."
• "Before I act, I want to confirm the measurement — with colour Doppler turned off, because colour over-diagnoses oligohydramnios — and I want to exclude ruptured membranes. She describes a gush that settled, which makes preterm prelabour rupture the leading cause."
• "At the bedside I would take a focused history, perform a sterile speculum, send nitrazine, ferning and a PAMG-1 (AmniSure) test; ultrasound alone is a poor test of rupture with a sensitivity around 19%."^[2]

Examiner is listening for: threshold, the method caveat (colour off, deepest pocket), and a structured differential by mechanism — under-production, loss, idiopathic. ^[2]

Probe 1 — "What is in your differential for oligohydramnios?"

• "By mechanism: under-production — renal agenesis or dysplasia, posterior urethral valves, placental insufficiency with growth restriction, postdates, maternal dehydration; loss — preterm or term prelabour rupture; and idiopathic."
• "The growth restriction here points me toward placental insufficiency, but the history of a gush makes rupture the priority to confirm. Oligohydramnios may also be the first sign of an undiagnosed renal anomaly in about 10% or an aneuploidy in about 13%, so I would complete the workup rather than reassure."^[2][5]

Probe 2 — "Now the polyhydramnios case. Define it and walk me through your management."

• "Polyhydramnios is a deepest vertical pocket of 8 cm or more, or an amniotic fluid index of 24 cm or more (SMFM #46). This is moderate disease (AFI 30)."
• "My workup is a detailed anatomy scan looking for a swallowing failure — gastrointestinal obstruction, CNS lesion, hydrops — a repeat 75 g glucose tolerance test, TORCH and antibody screen."
• "Management follows SMFM #46: amnioreduction only for severe maternal discomfort or dyspnoea in severe polyhydramnios; indomethacin not for the sole purpose of reducing fluid; mild idiopathic needs no surveillance; severe polyhydramnios to a tertiary centre."^[1]

Probe 3 — "She asks whether draining the fluid will fix it."

• "I would explain that amnioreduction is a temporiser, not a cure — the fluid re-accumulates, and repeat procedures carry PPROM, abruption and infection risk. The goal of the workup is to find and treat the cause; drainage is reserved for when the volume is causing her respiratory compromise."^[1]
• "I would also flag the birth risks of an overdistended uterus — malpresentation, PPROM, cord prolapse, abruption, preterm birth, and postpartum haemorrhage — and plan an active third stage with uterotonics ready."^[1][2]

Probe 4 — "Why do you use the deepest pocket rather than the amniotic fluid index?"

• "The Nabhan Cochrane pooled four trials and showed the amniotic fluid index over-diagnoses oligohydramnios (risk ratio 2.33), drives more inductions (RR 2.10) and more caesareans for fetal distress (RR 1.45), with no improvement in perinatal outcomes. For surveillance I use the single deepest pocket."^[3]

Probe 5 — "The oligohydramnios woman turns out to have had PPROM at 19 weeks. She asks if restoring the fluid will help the baby's lungs."

• "I would counsel her honestly. The PPROMEXIL-III randomised trial gave weekly transabdominal amnioinfusion to women with second-trimester PPROM and a deepest pocket under 20 mm and found no reduction in perinatal mortality — 64% versus 75%, relative risk 0.86. Amnioinfusion is not standard treatment for mid-trimester PPROM."
• "The real risk is pulmonary hypoplasia and limb deformity — the Potter sequence — and I would involve the maternal-fetal medicine and perinatal palliative teams for honest prognosis and surveillance."^[4][2]

Probe 6 — "How do you communicate the PPROM prognosis to her?"

This is a scored domain — demonstrate it out loud: ^[1]

• Sit at her level, use her name, and brief plainly: "Your waters broke early, which means the baby has very little fluid around them. That can affect how the lungs grow. We cannot replace the fluid in a way that has been shown to help, but we will watch closely and plan with you."
• Acknowledge uncertainty, allocate a staff member to support her and her partner, avoid jargon, and commit to a follow-up conversation and a written plan.^[1]