Which type of placentation is associated with increased risk for complications in twin pregnancies?

In twin pregnancies, the type of placentation significantly influences the risk for various complications. Mono/di placentation, where two fetuses share one placenta but have separate amniotic sacs, is associated with a higher incidence of complications compared to di/di placentation (two placentas and two amniotic sacs).

The reason mono/di placentation presents more risks includes the potential for twin-to-twin transfusion syndrome (TTTS), which occurs when blood supply is imbalanced between the two fetuses due to shared vascular connections within the placenta. This can lead to significant disparities in fetal growth and health outcomes. Additionally, the presence of one shared placenta can complicate monitoring and management during pregnancy, as issues affecting the placenta can impact both twins simultaneously.

While mono/mono placentation—where the twins share both the placenta and the amniotic sac—also carries significant risks, the recognition of mono/di placentation as more commonly problematic arises from its higher prevalence compared to mono/mono cases. Conjoined placentation is quite rare and presents unique complexities but is not as frequently encountered clinically as mono/di pregnancies.

In summary, mono/di placentation is linked to a greater risk of complications primarily due to the shared placenta's