Placental characteristics in uncomplicated monochorionic diamniotic twin pregnancies

Abstract

Objective To investigate the association between placental sharing,vascular anastomoses,cord insertion and perinatal outcome in uncomplicated monochorionic diamniotic (MCDA) placentas.Methods Between January 1,2012 and July 31,2013,60 uncomplicated (seclective fetal growth restriction,twin anemia-polycythemia sequence and twin-twin transfusion dyndrome) MCDA placentas were studied.These uncomplicated MCDA placentas were divided into the placenta equally shared group with placental territory discordance (PTD) ＜0.25 and the placenta unequally shared group with PTD ≥ 0.25.Angioarchitecture,cord insertion type and the distance between two cord insertions were compared using the Chi-square test and nonparametric test.Results Mean maternal age was (30.3±4.1) years.There were 39 cases (65％) in the placenta equally shared group and 21 (35％) in the placenta unequally shared group.Vascular anastomoses were observed in all placentas,arterioarterial anastomoses in 58 placentas (97％),and venovenous anastomoses in 17 placentas (28％).The overall diameter and the maximum diameter of arterioarterial anastomoses in the placenta equally shared group were (0.19±0.11) cm and (0.18±0.09) cm,respectively,and were lower than those in the placenta unequally shared group [(0.27±0.11) cm and (0.27±0.12) cm,respectively] (T were-2.39 and-2.94,P＜0.05,respectively).No significant differences in the number,the overall diameter and the maximum diameter of venovenous anastomoses were observed between the two groups (all P＞0.05).The incidence of cord velamentous insertion and cord velamentous insertion plus cord marginal insertion were 14％ (11/78) and 42％ (33/78),respectively,in the placenta equally shared group,and were similar to those in the placenta unequally shared group [14％ (6/42) and 33％ (14/42),x2 were 1.00 and 0.43,P＞0.05,respectively].The mean distance between two cord insertions was shorter in the placenta unequally shared group than in the placenta equally shared group [(14.3±6.3) cm vs (18.2±6.0) cm,T=2.37,P＜0.05].Conclusions In cases with unequally shared placenta,the distance between two cord insertions is shorter and the diameter of arterioarterial anastomoses is larger,which may compensate for their unequal placental territories,leading to no complications in these MCDA twin. Key words: Twin, monochorionic; Placental circulation; Umbilical arteries; Umbilical veins