FFinalistSouthampton · 2027
Obstetrics & gynaecology
AKT · Obstetrics & gynaecology/Antenatal & medicallow yield

Multiple pregnancy

Twins/higher-order (chorionicity-defined)

Overview

Pregnancy with more than one fetus. Chorionicity (determined by USS in the first trimester) drives risk — monochorionic twins share a placenta and risk twin-to-twin transfusion syndrome. Higher rates of all pregnancy complications.

Recognise

  • Large-for-dates uterus, hyperemesis (high hCG), more marked symptoms
  • USS: number of sacs/fetuses; "lambda/twin-peak" sign = dichorionic, "T-sign" = monochorionic
  • Risks: preterm birth, growth restriction, pre-eclampsia, anaemia, PPH

Red flags

  • Twin-to-twin transfusion syndrome (monochorionic); preterm labour; growth discordance

Differentials & how to tell them apart

Singleton with large-for-dates (macrosomia, polyhydramnios, fibroids)USS shows one fetus
Molar pregnancyvery high hCG, snowstorm USS

Investigations

First-trimester USS for chorionicity (crucial). Serial growth scans (more frequent for monochorionic). Screen for anaemia/pre-eclampsia.

Management

Chorionicity-based surveillance + aspirin from 12 weeks

  1. 1Determine chorionicity on first-trimester USS. Aspirin from 12 weeks; iron/folate; consultant-led care.
  2. 2Monochorionic: 2-weekly scans from 16 weeks (twin-to-twin transfusion). Plan timing/mode of delivery by chorionicity.
Aspirin from 12 weeks — pre-eclampsia prevention
Iron/folate — higher requirements

Key points

Chorionicity is the single most important determinant — monochorionic (shared placenta) carries the twin-to-twin transfusion risk and needs intensive surveillance.

Monitor & prognosis

Growth, liquor/discordance (monochorionic), pre-eclampsia, anaemia.

Good with surveillance; higher complication rates than singletons.

Source: NICE NG137 (twin/triplet pregnancy)