Abstract： Objective:To investigate the effect of placental vascular distribution on residual anastomoses (RA) after fetoscopic laser occlusion of chorioangiopagous ressels (FLOC) for twin to twin transfusion syndrome (TTTS).Methods:A total of 57 cases of TTTS after laser surgery were retrospectively analyzed from April 2014 to April 2019 in Peking University Third Hospital. The patients were divided into RA group (24 cases) and non-RA group (33 cases) according to whether RA occurred in the placenta after laser surgery. The clinical characteristics, perioperative conditions, pregnancy outcomes and placental structure characteristics of the two groups were compared. Multivariate logistic regression was used to analyze the risk factors of placental vascular distribution for RA. The RA group was further divided into non-remission group and remission group, and the placental characteristics and pregnancy outcome of the two groups were compared.Results:(1)General clinical characteristics: the age, application of assisted reproductive technology, incidence of gestational hypertension, gestational diabetes mellitus, preoperative maximum amniotic fluid depth of the donor and recipient twins, Quintero stage and placental position of TTTS patients in the two groups were compared respectively, and there were no statistically significant differences (all P>0.05).The gestational age of patients received FLOC in the RA group was significantly higher than the non-RA group [(23.0±2.4) vs (21.9±2.7) weeks, P=0.033].(2) Perioperative conditions and pregnancy outcomes: the delivery gestational age of the RA group was significantly lower than that of the non-RA group (median:31.8 vs 34.4 weeks, P=0.002);The newborn birth weight in the RA group was significantly lower than that in the non-RA group [(1 648±597) and (2 013±481) g, P=0.003].The birthweight difference in the RA group was significantly higher than that in the non-RA group (median:0.30 vs 0.11, P=0.005). (3) The placental structure and the risk factors influencing RA happened: the differences in the proportion of four types of placental vascular distribution in the RA group and non-RA group were different significantly ( χ2 =10.214, P=0.012), with a detail of parallel type 29% (7/24) and 3% (1/33), staggered type 58% (14/24) and 76% (25/33), hybrid 8% (2/24) and 21% (7/33), monoamniotic membrane type 4% (1/24) and 0 respectively. Multivariate logistic regression analysis showed that parallel placental vascular distribution was an independent risk factor for RA after FLOC ( OR=24.5, 95% CI 1.7-336.2, P=0.017). (4) Placental characteristics and pregnancy outcomes in the remission and non-remission groups of the RA group: the incidence of three kinds of anastomoses, the total number, total diameter and proportion of RA, and the placental territory discordance ratio were compared between the two groups, and there were no statistical significances ( P>0.05);The birth weight difference ratio in the non-remission group was higher than that in the remission group (median:0.41 vs 0.28, P=0.036). Conclusion:The parallel type of placental vascular distribution may be an independent risk factor for RA in TTTS after laser surgery.