Perinatal outcome, placental pathology, and severity of discordance in monochorionic and dichorionic twins

Objective: To evaluate differences in pregnancy outcomes and placental find ings among severely discordant monochorionic and dichorionic twins. Methods: We studied retrospectively a cohort of 382 twin pregnancies with g estational ages that ranged from 24 to 40 weeks. Pregnancies were classifie d as dichorionic or monochorionic by histologic examination of placentas. I nfants were subdivided into concordant (less than 5% difference in birth we ight), mildly discordant (5-25% difference), and severely discordant groups (more than 25% difference), and their clinical characteristics and finding s at placental examination were analyzed and compared. Results: Severe discordance occurred significantly more often in monochorio nic than in dichorionic twins and was associated with significantly more de liveries before 36 weeks and more newborns remaining more than 10 days in t he neonatal intensive care unit. Severely discordant monochorionic and dich orionic twins had significantly worse perinatal mortality and morbidity tha n mildly discordant and concordant twins. The weight of the placenta of the smaller fetus in severely discordant dichorionic twins with separate place ntas and the total placental weight in severely discordant monochorionic tw ins were significantly smaller than the weights of the placentas in their c oncordant and mildly discordant counterparts. The umbilical cords of the sm aller fetuses in both dichorionic and monochorionic pregnancies exhibited s ignificantly more velamentous insertions and single umbilical arteries than in concordant or mildly discordant twins of similar chorionicity. Conclusion: Severe discordance is more frequent and has greater morbidity i n monochorionic than dichorionic twins. The most frequent findings in the p lacentas of severely discordant twins were small placental weight and umbil ical cord abnormalities. (Obstet Gynecol 2001;97:310-5. (C) 2001 by The Ame rican College of Obstetricians and Gynecologists.).