Risks of obstetric complications in multiple pregnancies: an analysis of more than 400 000 pregnancies in the UK

This study aims to provide estimates of risk for common obstetric complicat ions in multiple pregnancies compared to singletons, and to calculate estim ated risks in monochorionic compared to dichorionic twin pregnancies with s ame-sex and different-sex twin data, using a retrospective review of a vali dated obstetric database (SMMIS) derived from maternity units in the North West Thames Region of London, UK. There were 423 107 pregnancies resulting in live births or stillbirths at greater than or equal to 24 weeks of gesta tion, including 417 542 singleton, 5416 twin (1.3%) and 149 triplet pregnan cies (0.03%). The twin pregnancies included 1853 (34.2%) different-sex and 3563 (65.8%) same-sex pregnancies. Comparison of pregnancy outcome was made on the basis of number of fetuses present, and whether the fetuses were of the same sex or different sex. Antenatal complications, intervention in la bor, maternal morbidity and neonatal outcomes were determined. Data are pre sented as frequency of outcomes in the groups and logistic regression analy sis was then carried out to provide adjusted odds ratios and 95% confidence intervals for each outcome. Several pregnancy complications were more freq uent in multiple compared to singleton pregnancies. These included pre-ecla mpsia, antepartum hemorrhage, anemia, delivery by Cesarean section, preterm delivery, low birth weight, stillbirth, admission to the neonatal intensiv e care unit, postpartum hemorrhage and maternal infective complications. Th e only outcomes significantly more frequent in same-sex compared to differe nt-sex pregnancies were preterm delivery and low birth weight. For most of these variables, the magnitude of risk increased with the number of fetuses .