Monochorionic monoamniotic twin pregnancies.

Abstract Monoamniotic twins are rare, but their early diagnosis is critical, as the incidence of complications in these pregnancies is much higher than in diamniotic or dichorionic twin pregnancies. Overall, only 70% of all monoamniotic twins will survive. About half of the fetal deaths is due to the high incidence of fetal anomalies (15-25%), twin reversed arterial perfusion sequence and conjoined twinning. Early anatomy screening in the first trimester of pregnancy is therefore recommended. The remainder of fetal losses are due to twin-twin transfusion syndrome, tight cord entanglement or acute hemodynamic imbalances through the large placental vascular anastomoses. After viability, fetal surveillance can be intensified, as this decreases the risk of in-utero death. Both inpatient and outpatient surveillance are reasonable. If otherwise uncomplicated, monoamniotic twins should be delivered by 33-34 weeks gestation. Most centers will deliver by cesarean section, but some still continue to advocate for vaginal delivery. Neonatal morbidity is high, and mainly related to prematurity.