Differences in umbilical vein predict placental sharing and outcome in monochorionic twins with selective growth-restriction

To examine the association between umbilical venous diameters and flow with placental sharing and adverse outcomes in monochorionic twin pregnancies diagnosed with selective fetal growth restriction (sFGR). The venous placental territory determines the oxygenated blood flow to the fetuses. Unequal placental sharing is considered the main contributor but is not yet quantifiable during pregnancy. Prospective cohort study of monochorionic diamniotic twin pregnancies diagnosed with sFGR. The following ultrasound variables were measured: intra-abdominal and free loop diameter of the umbilical vein (UV), estimated fetal weight (EFW), and cord insertions. The time-averaged maximum velocity in the intra-abdominal UV was measured and used to calculate UV-flow. Ratios (larger/smaller twin) were used for analysis. Adverse outcome was defined as the occurrence of fetal demise or birth before 34 weeks. We included 102 consecutive sFGR pregnancies, of which 88 placentas (86%) underwent injection studies with barium sulfate. The overall survival was 89%: 7 cases with single fetal demise (7%), 5 with double demise (5%), and 5 neonatal deaths (5%) occurred. Univariable linear regression analysis showed a significant association for all of the variables with placental sharing. In multivariable analysis, the UV-variables and a discordant cord insertion remained significantly associated with placental sharing. EFW differences and a concordant or intermediate cord insertion were not significantly associated with placental sharing. Logistic regression and receiver operating characteristics curve analysis demonstrated that EFW discordance and the cord insertion site had a poor predictive accuracy for an unequally shared placenta or an adverse outcome. In contrast, the predictive accuracy of the UV-variables was fair. Differences in UV-diameter and flow between the twins at the time of sFGR diagnosis inform us of the placental sharing, more so than differences in EFW. Differences in UV-variables between the twins also seem to increase the risk of fetal demise and birth before 34 weeks.View Large Image Figure ViewerDownload Hi-res image Download (PPT)