[Placental specific findings in twin pregnancies with hydramnion].

Eleven of 157 twin pregnancies were complicated with polyhydramnios. Chorionicity, vascular anastomosis and insertion of the umbilical cord were analyzed with relation to polyhydramnios. 1. Polyhydramnios was found commonly in monochorionic placentation. 2. Vascular anastomosis was found in 40% of monochorionic polyhydramnotic placentas, which was lower than the anastomosis of monochorionic non-polyhydramniotic placentas. 3. The placentas with hydramnios had a higher incidence of abnormal umbilical insertion (marginal or velamentous insertion). These data indicate that incompetent vascular connections between the two fetoplacental circulations may be the pathogenesis of polyhydramnios.