Velamentous cord insertion and unequal placental territories in monochorionic twins with and without twin-to-twin-transfusion syndrome.

OBJECTIVE The objective of this study was to determine the incidence of velamentous cord insertion and placental territory discordancy in monochorionic twins with and without twin-to-twin transfusion syndrome (TTTS). STUDY DESIGN All consecutive placentas of monochorionic twins delivered at our center between June 2002 and April 2006 were studied with vascular injection of the umbilical vessels with colored dyes. Velamentous cord insertions were recorded and individual placental territories were calculated by computer analysis. RESULTS A total of 76 monochorionic placentas with TTTS and 63 monochorionic placentas without TTTS were studied. The incidence of velamentous cord insertion (per fetus) in the TTTS group and the non-TTTS group was 13% (20 of 152) and 14% (18 of 126), respectively (P = .79). Placental territory discordancy in the TTTS group and the non-TTTS group was 20% and 20% (P = 0.83). In the TTTS group, donor twins had a velamentous cord insertion more often than recipient twins (24% and 3%, respectively, P < .001) and a smaller placental territory (44% and 56%, respectively, P < .001). CONCLUSION Our findings suggest that velamentous cord insertion and unequal placental territory are not critical factors for the development of TTTS.