What are the rates and mechanisms of first and second trimester pregnancy loss in twins

Pathologic, ultrasonographic, and biochemical evidence all lead to the conclusion that the majority of twin pregnancies are lost before delivery and that the majority of these losses occurs within the first half of the initial trimester. Moreover, twin conceptions are lost at a greater rate than their singleton counterparts. These realities underscore the fact that twinning must be more common an event than liveborn demographics indicate. Despite consensus on these points, the exact proportion of surviving twin pregnancies remains a matter of debate. Different authors have propounded different frequencies of loss, with estimates ranging up to 98% of all twin conceptions. Multiple etiologies have been proposed to explain the loss of twin gestations during the first and second trimester. Several therapeutic methods have been advocated in an attempt to prevent second-trimester loss. Although some are promising, further research and randomized, controlled trials are necessary to prove their benefits.