Monochorionic twin gestation complicated by a sacrococcygeal teratoma with hydrops--optimal timing of delivery allows for survival of the unaffected twin.

Sacrococcygeal teratomas are the most common tumors found in newborns and have a favorable outcome when diagnosed late in gestation. Solid, highly vascularized tumors diagnosed early in gestation have a higher incidence of hydrops fetalis and fetal demise. The following is a case report of a monochorionic twin gestation complicated by a solid highly vascular sacrococcygeal teratoma and the development of hydrops in the affected twin. In this case, serial ultrasound evaluations and timing of delivery optimized the outcome of the unaffected twin.