AbstractFetal malformations are more frequent in twins than in singletons. The aim of our study was to define the influence of a malformed twin on di-chorionic pregnancy outcomes. We performed a retrospective cohort study of di-chorionic pregnancies delivered between 2000 and 2015. Exclusion criteria were: both twins affected by fetal malformations, double intra-uterine fetal death in pregnancies without fetal malformation, selective feticide and therapeutic pregnancy termination. We compared maternal and fetal outcomes of di-chorionic pregnancies not complicated by fetal malformations with pregnancies affected by a single malformed fetus with conservative management. We included 642 di-chorionic pregnancies: 56 (case group, 8.7%) with one twin affected by a malformation (20 minor, 36 major ones), 586 (control group, 91.3%) without fetal malformation. No differences were found on maternal and not malformed co-twin outcomes when compared to pregnancies with no malformation; case vs control group presented similar rates of preeclampsia (8.9% vs. 10.8%, respectively), intrauterine growth restriction (7.1% vs. 9.4%) and composite adverse neonatal outcomes (19.6% vs. 15.1%). No case of fetal death in not malformed co-twin was reported. Expectant management could be a safe option for both mother and co-twin in case of di-chorionic twin pregnancy complicated by only one malformed fetus.