Placental angioarchitecture in monochorionic twin pregnancies: Relationship to fetal growth, fetofetal transfusion syndrome, and pregnancy outcome

OBJECTIVE: We sought to correlate placental vasculature with fetal growth a nd outcome in monochorionic twins. STUDY DESIGN: Eighty-two patients with consecutive monochorionic pregnancie s underwent biweekly ultrasonography for determination of fetal growth and well-being. After delivery, blinded placental injection studies delineated vascular anastomoses and territory share. Degree of balance in arteriovenou s anastomoses equaled the number of arteriovenous anastomoses in one direct ion minus the number in the other. RESULTS: Pregnancies affected by fetofetal transfusion syndrome (n = 21) ha d numbers of arteriovenous and venovenous anastomoses that were similar to those in pregnancies without fetofetal transfusion syndrome but fewer arter ioarterial anastomoses (P < .0001). Fetofetal transfusion syndrome occurred in 78% of pregnancies with 21 arteriovenous and no arterioarterial anastom oses. Birth weight discordancy correlated with placental territory discorda ncy (P < .0001) and the degree of balance in arteriovenous anastomoses (P = .004). The larger placental share twin had a greater growth velocity than its smaller placental share cotwin (P = .008) for all but one anastomotic p attern. Where arteriovenous anastomoses were aligned with the net venous ou tflow to the fetus with the smaller territory, co-twins had similar birth w eights and growth velocities irrespective of placental share. Fetal surviva l was higher in pregnancies with an arterioarterial anastomosis (P = .01) b ut lower with a venovenous anastomosis (P = .01). Survival of both fetuses was inversely associated with birth weight discordancy (P < .0001). CONCLUSION: Although interrelationships among the various types of anastomo ses are complex, our data suggest that the placental territory share and th e pattern of arteriovenous anastomoses influence fetal growth, that arterio arterial anastomoses protect against fetofetal transfusion syndrome, and th at venovenous anastomoses reduce perinatal survival.