Risk of cerebral palsy in multiple pregnancies.

Multiple compared with singleton gestations have a five- to tenfold increased risk of CP. The increased risk associated with MC placentation has been variously ascribed to transfer of thromboplastin or thromboemboli from the dead to the surviving fetus, exsanguination of the surviving fetus into the low pressure reservoir of the dead fetus, or hemodynamic instability with bidirectional shunting of blood between the two fetuses. An increased risk of CP in assisted reproductive technology gestations is to be expected because of the higher proportion of preterm births. The increase in risk of CP associated with monochorionic placentation will not be observed except for the minority of assisted reproductive technology gestations that undergo monozygotic splitting.