PROGNOSTIC-SIGNIFICANCE OF PRIOR PRETERM TWIN DELIVERY ON SUBSEQUENT SINGLETON PREGNANCY

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 Ca rolina perinatal database was accessed to identify a cohort of patient s 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 wit h 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 t wins was associated with a significantly increased risk of preterm del ivery in a subsequent singleton pregnancy (relative risk 2.87, 95% con fidence interval 1.02 to 8.09). In the subset of women who were delive red 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% co nfidence interval 1.02 to 12.92). However, if the preceding twins deli vered between 34 and 37 weeks' gestation, the relative risk of preterm birth of the subsequent singleton was not significantly increased (re lative 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 pregn ancy. The magnitude of risk increases with decreasing gestational age of the preceding twin delivery.