Objective: Our purpose was to determine whether preterm birth of twins is associated with an increased risk of preterm birth in a subsequent singleton pregnancy.
Study design: The Medical University of South Carolina perinatal database was accessed to identify a cohort of patients who were delivered of twins followed by a singleton gestation (1981 to 1993). Maternal transports were excluded to minimize referral bias. Preterm birth was defined as < 37 weeks' gestation. Relative risks with 95% confidence intervals were calculated.
Results: One hundred forty-four patients were identified who were delivered of twins followed by a singleton gestation. Preterm delivery occurred in 86 (59.7%) of the twins and 21 (14.6%) of the subsequent singletons. Preterm birth of twins was associated with a significantly increased risk of preterm delivery in a subsequent singleton pregnancy (relative risk 2.87, 95% confidence interval 1.02 to 8.09). In the subset of women who were delivered of twins at < 30 weeks' gestation, 42% of the subsequent singletons were delivered preterm (relative risk 6.11, 95% confidence interval 2.07 to 18.02). The relative risk of preterm birth of a singleton after delivery of twins between 30 and 34 weeks' gestation was 3.63 (95% confidence interval 1.02 to 12.92). However, if the preceding twins delivered between 34 and 37 weeks' gestation, the relative risk of preterm birth of the subsequent singleton was not significantly increased (relative risk 1.42, 95% confidence interval 0.40 to 5.01).
Conclusions: Preterm birth of twins before 34 weeks' gestation is associated with a significant risk for preterm delivery in a subsequent singleton pregnancy. The magnitude of risk increases with decreasing gestational age of the preceding twin delivery.