The vascular equator in monochorionic twin placentas

INTRODUCTION: We aim to examine the location of the vascular equator according to the umbilical cord insertions in monochorionic twin placentas. METHODS: We combined two prospective series of monochorionic diamniotic twin placentas of patients included in the first trimester between 2004 and 2008, and between 2016 and 2019. We injected the placentas after birth and divided them into three groups, with respectively concordant (eccentric-eccentric, marginal-marginal, and velamentous-velamentous), intermediate (eccentric-marginal and marginal-velamentous) and discordant (eccentric-velamentous) cord insertions. For each unidirectional anastomosis, we determined the cord-anastomosis ratio and then calculated the mean ratio per placenta in each group. We also calculated the deviation from the midline in all groups. RESULTS: 195 placentas were included. In concordant placentas, the mean cord-anastomosis ratio was 0.957 (95% CI [0.908-1.009]). In placentas with intermediate discordance, the mean ratio was 0.886 (95% CI [0.828-0.948]) and in discordant placentas it was 0.797 (95% CI [0,708-0.897]) (p