Obstetrics

Multiple Pregnancy

Twin and triplet pregnancy is higher risk than singleton pregnancy; early determination of chorionicity and amnionicity drives surveillance, fetal-medicine referral, preterm-birth prevention and timing and mode of birth.

In a nutshell

Multiple pregnancy is managed by chorionicity and amnionicity. Determine these early, label the fetuses, provide specialist surveillance and refer monochorionic complications promptly. NICE recommends cervical-length screening at 16–20 weeks, vaginal progesterone when the cervix is 25 mm or less, and planned birth at 37 weeks for uncomplicated DCDA twins, 36 weeks for MCDA twins, 32+0–33+6 weeks for MCMA twins and 35 weeks for uncomplicated trichorionic or dichorionic triamniotic triplets.

Classic presentation

A first-trimester scan shows monochorionic diamniotic twins. Document the T-sign and fetal labels, arrange fortnightly surveillance from 16 weeks, screen cervical length at 16–20 weeks, assess pre-eclampsia risk and plan birth at 36 weeks if uncomplicated.

Key points

Chorionicity and amnionicity, not zygosity, determine risk and surveillance.
Monochorionic complications include TTTS, selective growth restriction and TAPS.
Offer cervical-length screening at 16–20 weeks and vaginal progesterone for a cervix 25 mm or less.
Offer aspirin only when NICE pre-eclampsia risk criteria are met; multifetal pregnancy is one moderate risk factor.
Planned birth: DCDA twins 37 weeks, MCDA twins 36 weeks, MCMA twins 32+0–33+6 weeks and uncomplicated triamniotic triplets 35 weeks.

First-line investigation

First-trimester ultrasound to determine gestational age, chorionicity, amnionicity and consistent fetal labels, followed by chorionicity-specific scans.

Management

Classify and label

Determine gestational age, chorionicity and amnionicity at the first scan, label each fetus consistently and manage uncertain classification as monochorionic until clarified.¹

Start specialist surveillance

Use the NICE schedule for the pregnancy type, watch for discordant fluid, growth and Doppler findings, and refer monochorionic complications to tertiary fetal medicine.¹

Prevent maternal and preterm complications

Offer cervical-length screening and vaginal progesterone when indicated; assess aspirin eligibility and monitor blood pressure, urine protein and anaemia.^1,2,3

Plan birth and haemorrhage precautions

Offer chorionicity-specific planned birth, individualise complicated pregnancies, agree mode from presentation and complications, and ensure CTG, intravenous access, blood availability and active third-stage management.^1,4

Exam traps

Monozygotic twins can be dichorionic; zygosity is not the management classification.
TTTS requires shared placental circulation.
If chorionicity remains uncertain, manage as monochorionic until proven otherwise.
Do not give routine untargeted corticosteroids solely because the pregnancy is multiple.
Uncomplicated twins with a cephalic first twin after 32 weeks can choose planned vaginal birth or caesarean; monoamniotic twins and triplets differ.

Illustrations

Lambda versus T-signFirst-trimester ultrasound comparing the lambda sign of dichorionic twins with the T-sign of monochorionic diamniotic twins, with a note that amnionicity must also be established.Khalil A et al., Ultrasound in obstetrics & gynecology 2025, CC-BY-4.0 · CC-BY-4.0

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.