Roles of venovenous anastomosis and umbilical cord insertion abnormalities in birthweight discordance in monochorionic-diamniotic twin pregnancies without twin-twin transfusion syndrome

AimWe evaluated risk factors for birthweight discordance in monochorionic diamniotic (MCDA) twin pregnancies without twin-twin transfusion syndrome (TTTS). MethodsWe investigated all MCDA twin placentas injected with colored dye at our institution between 2007 and 2015. We excluded pairs of twins with TTTS, fetal demise, or severe fetal malformation. All pairs of twins were assigned to the discordant group (birthweight discordance25%) or the concordant group (birthweight discordance<25%). In each pair of twins, we described vascular anastomoses as either arterioarterial, venovenous (VV), or arterial-venous, and abnormal umbilical cord insertion as either marginal or velamentous. We also recorded placental sharing discordance. ResultsA total of 150 placentas were analyzed. The incidence of VV anastomosis in the discordant group (40%) was significantly higher than that in the concordant group (12%, P=0.005). Unilateral abnormal umbilical cord insertion was significantly more common in the discordant group (85%) than in the concordant group (38%, P<0.001). Placental sharing discordance was seen more frequently in the discordant group than in the concordant group. Multiple logistic analysis revealed that VV anastomosis (odds ratio: 4.7; 95% confidence interval: 1.2-18.6, P<0.01) and unilateral abnormal umbilical cord insertion of the smaller twin (odds ratio: 5.7; 95% confidence interval: 1.4-22.9, P<0.01) were independent risk factors for birthweight discordance. ConclusionVV anastomoses and unilateral abnormal umbilical cord insertion of the smaller twin are independent risk factors for birthweight discordance in MCDA twin pregnancies without TTTS.