Perinatal outcomes in singleton and twin pregnancies following first-trimester bleeding.
To investigate associations between first-trimester bleeding and perinatal outcomes. Registry-based survey of the period 2002 through 2010. Pregnancies with versus without first-trimester bleeding were compared using Student's t- and χ(2)-test. Multivariable logistic regression was used to control for potential confounders. 9924 singleton and 275 twin pregnancies with first-trimester bleeding, and 160 099 singleton and 2710 twin pregnancies without bleeding were included. Bleeding increased the risk of preterm birth in singletons (odds ratio 1.48; 95% confidence interval 1.38-1.60). Risks were also increased for preterm premature rupture of membranes, abruption, previa, stillbirth and congenital anomalies, with a reduced risk of preeclampsia. The differences remained significant after adjustment for confounders. In twin pregnancies, bleeding was not significantly associated with prematurity (odds ratio 1.04; 95% confidence interval 0.81-1.34), nor with other outcomes. In singletons, but not in twins, the risk of perinatal complications is significantly increased after first-trimester bleeding.