Ultrasound observations in multiple gestation with first trimester bleeding: the blighted twin.

Twenty-two patients, 19 of whom presented with first trimester bleeding, underwent ultrasound examination demonstrating a normal amniotic cavity containing a fetus with regular heart activity. In each, a separate anechoic or hypoechoic region was identified within the uterus compatible with a coexistent anembryonic pregnancy or "blighted twin." Three patterns, (a) second sac, (b) crescent of fluid outlining the intact sac, and (c) septal division of the amniotic cavity with one compartment empty, are described. Seven additional cases showing variant situations are discussed. The diagnosis of blighted twin carries a good prognosis for carrying the single gestation to term.