Monochorionic Monoamniotic Twin Pregnancy

Monochorionic monoamniotic (MCMA) twins share one placenta and one amniotic sac, from division of the embryo after day 8 to 9. They are about 1% of monozygotic twins (about 1 in 10,000 pregnancies) and form the highest risk twin pregnancy.

Cord entanglement is almost universal (70 to 100%), with risk of acute cord compression and sudden fetal death (10 to 15% historically with expectant management), twin-to-twin transfusion (5 to 10%), congenital anomalies (15 to 20%, including conjoined twins and twin reversed arterial perfusion), preterm birth, and neurological injury of the survivor after single twin death.

• Usually asymptomatic; vigorous fetal movement
• Episodes of reduced fetal movement may signal cord compression
• Entangled cords on ultrasound with tangled colour Doppler
• Maternal polyhydramnios and preterm contractions
• Fetal anomalies: structural defects, conjoined twins

• Absence of an inter twin membrane on first trimester ultrasound (confirmed by 10 to 14 weeks), one placenta, entangled cord loops, and pulsed Doppler showing two distinct arterial waveforms at different heart rates within the same cord mass
• Early anomaly scan with detailed cardiac assessment (fetal echocardiography at 18 to 22 weeks)
• Growth scans every 2 weeks (growth discordance, fluid, Doppler)
• Karyotype or microarray of both fetuses when anomalies are present

• Counsel at diagnosis about the high perinatal mortality risk and the care pathway
• Surveillance is intensive: cardiotocography once or twice weekly from viability (24 to 26 weeks) with ultrasound every 2 weeks; many centres admit from 26 to 28 weeks for daily monitoring, which allows emergency caesarean if the tracing deteriorates
• Betamethasone 12 mg IM, two doses 24 hours apart, at 26 to 28 weeks, with a repeat course if delivery is still pending at 32 weeks according to local practice. Sulindac 200 mg twice daily has been used to reduce amniotic fluid and fetal movement in cord entanglement, but it is unproven and needs ductal monitoring
• Delivery: planned caesarean at 32 to 34 weeks (32 weeks 0 days to 33 weeks 6 days), earlier for abnormal cardiotocography, Doppler or new complications. Vaginal delivery is not advised because of cord accident risk
• Neonatal intensive care, cranial imaging and developmental follow up
• If twin-to-twin transfusion develops, fetoscopic laser coagulation of the placental anastomoses between 16 and 26 weeks is the treatment (technically harder in a shared sac), with selective cord occlusion in some cases. If twin reversed arterial perfusion occurs, radiofrequency ablation or cord coagulation of the acardiac twin at 12 to 16 weeks protects the pump twin
• Single twin death: urgent delivery assessment depending on gestation, and MRI of the survivor 2 to 4 weeks later for ischaemic injury