Induction of labor: comparison of a cohort with uterine scar from previous cesarean section vs. a cohort with intact uterus.

Objective: To compare the risk of uterine rupture between a cohort of women with previous low-transverse cesarean section (CS) and a cohort with intact uterus.
Methods: All women with a singleton pregnancy and previous low-transverse CS requiring induction of labor from January 1, 1992 to December 30, 2001 (n = 310) were compared with a cohort of women with intact uterus undergoing induction of labor during the same study period (n = 5420). Protocols of induction using prostaglandin E2 gel and oxytocin infusion were consistent within groups, but differed between the previous CS and the intact uterus group.
Results: Uterine rupture occurred in 0.3% in the previous CS group vs. 0.03% in the intact uterus group (p = 0.37). Logistic regression analysis showed no significant difference in rate of uterine rupture between the previous CS vs. intact uterus group (p = 0.16) after controlling for maternal age, parity, gestational age at delivery, Bishop score on admission, use of prostaglandin and oxytocin, and birth weight. Our study had adequate power to detect a 0.38% difference in rate of uterine rupture between the two groups (alpha = 0.05, beta = 0.80).
Conclusion: Induction of labor is not associated with significantly higher rates of uterine rupture among women with previous low-transverse CS compared with women with intact uterus provided a consistent protocol with strict intervention criteria is adopted.