Incidence and clinicopathologic correlation of fetal vessel thrombosis in mono- and dichorionic twin placentas

Objective:to determine the incidence of fetal vessel thrombosis in monochorionic-diamniotic and dichorionic-diamniotic twin placentas, and its association with intrauterine growth retardation (iugr), hypertensive disorders of pregnancy, twin–twin transfusion syndrome (ttts), fetal vascular anastomoses, chorangiosis, and chorioamnionitis.study design:histologic slides from 80 pairs of monochorionic and 80 pairs of dichorionic twin placentas were reviewed for evidence of fetal vessel thrombosis (⩾5 adjacent avascular terminal villi with upstream intravascular fibrin thrombi). associations with clinical and other pathologic variables were analyzed by χ2 tests.result:thrombosis occurred in 7.5% of monochorionic and 3.1% of dichorionic twin placentas (p=0.090). it was associated with iugr among the monochorionic twins (p=<0.0001) and with hypertensive disorders of pregnancy among the dichorionic twins (p=0.018). vascular anastomoses, ttts, chorangiosis, and chorioamnionitis were not associated with fetal vessel thrombosis.conclusion:fetal vessel thrombosis was identified more frequently in monochorionic twins, but this difference was not statistically significant. it is associated with iugr in monochorionic twins, but not with ttts or fetal vascular anastomoses at the chorionic surface.