Multiple pregnancy — chorionicity and surveillance — structured oral station (12 minutes)

Opening prompt — "You have scanned this woman at 11 weeks and found a single placenta with a T-sign. Tell me what this means and what you will do."

Model response: ^[1][6]

• "This is a monochorionic diamniotic twin pregnancy — the single placenta with a T-sign (the membrane inserting flat onto the placenta with no triangular projection) confirms it. The presence of an inter-twin membrane tells me it is diamniotic, not monoamniotic."
• "Chorionicity drives everything from here. I would document it clearly, and counsel her that monochorionic twins carry a higher risk than dichorionic twins because of the shared placental circulation."

Probe 1 — "What is your surveillance plan?"

• "Monochorionic diamniotic twins need 2-weekly growth scans from 16 weeks, with amniotic fluid (deepest vertical pool) and Doppler at each visit. This is more intensive than dichorionic twins, which get 4-weekly scans from 20 weeks."^[1]
• "I am screening for twin-twin transfusion syndrome, twin anaemia polycythaemia sequence, and selective fetal growth restriction. TTTS is the time-critical one — polyhydramnios in the recipient with oligohydramnios in the donor — and I would refer urgently to fetal medicine if I found it."^[5]

Probe 2 — "When will you deliver her, if all goes well?"

• "For uncomplicated monochorionic diamniotic twins, planned birth is from 36 weeks and no later than 37, because the stillbirth risk rises after 36 weeks even with reassuring surveillance."^[1]
• "That is earlier than dichorionic twins, which are delivered from 37 weeks supported by the Twins Timing of Birth Trial."^[3]

Probe 3 — "Her first twin is cephalic. Can she have a vaginal birth?"

• "Yes. The Twin Birth Study (Barrett, NEJM 2013) randomised over 2800 women with twins and twin 1 cephalic to planned caesarean versus planned vaginal, and found no difference in neonatal mortality or morbidity."^[2]
• "I would offer her planned vaginal birth, provided there is a skilled team, continuous monitoring of both twins in labour, and immediate access to theatre. The choice is hers after counselling."

Probe 4 — "She has heard that progesterone prevents premature birth and asks for a prescription. What do you say?"

• "Progesterone prevents preterm birth in some singleton pregnancies, but it does NOT work in twins. The Cochrane overview found no benefit in multiple pregnancy, and I would not prescribe it for that indication."^[4]

Probe 5 — "Counsel her on the maternal risks and how you will manage them."

Communication is a scored domain. ^[1]

• "Twin pregnancy raises your risk of high blood pressure and pre-eclampsia, diabetes, anaemia, and bleeding after birth. I will check your blood pressure and urine at every visit, prescribe low-dose aspirin for pre-eclampsia prevention, check your blood count for anaemia, do a diabetes test at 24 to 28 weeks, and plan for a safe birth with the right team."
• "I would also talk about your mental health, breastfeeding support, and the practical support you will need with two babies."