Twin and Triplet Pregnancy

Chorionicity Determination

• Must be determined at 11-13+6 week dating scan — most accurate time
• DCDA (dichorionic diamniotic): two placentae, two amniotic sacs — "lambda/twin peak sign"
• MCDA (monochorionic diamniotic): one placenta, two amniotic sacs — "T sign"
• MCMA (monochorionic monoamniotic): one placenta, one amniotic sac — no dividing membrane
• All monochorionic twins are monozygotic (identical); dichorionic can be monozygotic (30%) or dizygotic (70%)
• Chorionicity determines risk level, monitoring schedule, and delivery timing

Monitoring Schedules

DCDA Twins

• At least 8 antenatal appointments with the core team; combine with growth scans at 20, 24, 28, 32 and 36 weeks (plus non-scan appointments at 16 and 34 weeks) — i.e. growth USS roughly every 4 weeks from 20 weeks
• Monitor for discordant growth (inter-twin weight discrepancy >25%)
• Standard antenatal care with more frequent appointments

MCDA Twins

• At least 11 antenatal appointments with the core team; combine with scans at 16, 18, 20, 22, 24, 26, 28, 30, 32 and 34 weeks — i.e. USS every 2 weeks from 16 weeks (growth + Doppler + amniotic fluid)
• Primary surveillance for TTTS/FFTS (twin-to-twin/feto-fetal transfusion syndrome): every 14 days from 16 weeks until birth
• Refer to a tertiary fetal medicine centre if deepest vertical pool (DVP) is <2cm in one twin and >8cm (before 20+0 weeks) or >10cm (from 20+0 weeks) in the other
• Look for: discordant amniotic fluid (polyhydramnios/oligohydramnios), discordant growth, abnormal Dopplers

MCMA Twins

• Very high risk — inpatient monitoring from 24-26 weeks in many centres
• Daily CTG from viability
• USS every 2 weeks
• Risk of cord entanglement (unique to MCMA)

Twin-to-Twin Transfusion Syndrome (TTTS)

• Affects 10-15% of MCDA pregnancies
• Caused by unbalanced blood flow through placental vascular anastomoses
• Donor twin: anaemic, growth-restricted, oligohydramnios (stuck twin)
• Recipient twin: polycythaemic, fluid overloaded, polyhydramnios, hydrops

Quintero Staging

Treatment

• Fetoscopic laser ablation of placental anastomoses: definitive treatment for stages II-IV
• Performed at specialist fetal medicine centres
• Survival: ~70-80% for at least one twin, ~50-60% for both
• Amnioreduction: palliative/temporising measure — drainage of excess amniotic fluid
• Septostomy: rarely performed

Preterm Birth Prevention (2024 update)

• Offer a single cervical length scan between 16 and 20 weeks
• If cervical length is ≤25mm, discuss that vaginal progesterone may reduce the risk of preterm birth
• Offer vaginal progesterone 200mg once daily (bedtime) if cervical length ≤25mm; continue until 34 weeks
• Do NOT offer intramuscular progesterone for prevention of spontaneous preterm birth in twin/triplet pregnancy
• Do NOT routinely offer Arabin pessary, bed rest, cervical cerclage, or oral tocolytics for prevention of spontaneous preterm birth

Selective Intrauterine Growth Restriction (sIUGR)

• Inter-twin estimated fetal weight discordance ≥25%
• In MCDA twins: higher risk due to shared placenta
• Monitoring: frequent USS + Doppler, individualise based on severity
• Severe cases: consider selective feticide (cord occlusion) or early delivery

Timing of Delivery

• Corticosteroids if preterm delivery anticipated
• Neonatal team should be present at all twin deliveries

Mode of Delivery

• DCDA / MCDA: vaginal delivery can be offered if twin 1 is cephalic
• MCMA: caesarean section usually recommended
• Twin 1 non-cephalic: caesarean section
• Twin 2 management after delivery of twin 1: if cephalic — ARM and oxytocin if needed; if non-cephalic — internal podalic version and breech extraction (or caesarean)
• Experienced obstetrician should supervise twin vaginal deliveries

Important Facts for MRCOG

• Chorionicity MUST be determined at 11-13+6 weeks (lambda vs T sign)
• MCDA: scan every 2 weeks from 16 weeks (TTTS surveillance)
• TTTS: Quintero staging I-V
• Fetoscopic laser is definitive TTTS treatment (stages II-IV)
• Delivery timing: DCDA 37 weeks, MCDA 36 weeks, MCMA 32-33 weeks
• MCMA: caesarean section due to cord entanglement risk
• Inter-twin weight discordance ≥25% = significant growth restriction
• Single fetal demise in MCDA: ~15-20% risk of death or injury to co-twin (via acute haemodynamic shift through anastomoses)
• 2024 update: offer single cervical length scan at 16-20 weeks; if ≤25mm, offer vaginal (not IM) progesterone until 34 weeks — cerclage/pessary/bed rest/tocolytics NOT routinely offered

Source: NICE NG137 ("Twin and triplet pregnancy") (Published 4 September 2019; last reviewed/amended 9 April 2024 (new recommendations on screening for and preventing preterm birth))

Read the original on nice.org.uk

Clinically reviewed by NHS obstetricians and gynaecologists · Source last updated Published 4 September 2019; last reviewed/amended 9 April 2024 (new recommendations on screening for and preventing preterm birth)

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