Importance: Monochorionic (MC) twins are hemodynamically connected by vascular anastomoses within the single shared placenta. The transfer of fluid or blood from one fetus to the other may result in development of pathologic complications, such as twin-twin transfusion syndrome, twin anemia polycythemia sequence, selective intrauterine growth restriction, and twin reversed arterial perfusion sequence. Monoamniotic gestations, which comprise a small fraction of MC pregnancies, can also present with unique challenges, particularly antepartum umbilical cord entanglement. All these complications carry a high risk of fetal morbidity and mortality if not recognized and managed in a timely fashion.
Objective: The purpose of this article is to review evidence-based management of complicated MC twin gestations and propose a standardized approach to surveillance.
Evidence acquisition: Monochorionic gestations account for the majority of complications that occur in twin pregnancies; however, there is unclear evidence on the appropriate surveillance for and management of specific complications associated with these pregnancies.
Results: This article summarizes management for each specific type of MC complication in a structured and clear manner.
Conclusions: Early pregnancy ultrasound, ideally between 10 and 13 weeks' gestation, is critical for the diagnosis and characterization of twin pregnancies. To improve outcomes for MC twins, appropriate fetal surveillance should be initiated at 16 weeks' gestation and continued until delivery.