I. Induction of labor and maternal outcomes in multiparous women in a population-based sample

BACKGROUND: Induction of labor is associated with increased risks of cesarean section and vaginal birth with instrumentation (vacuum or forceps) in nulliparous women. Less is known about the association between induction of labor and cesarean section and vaginal birth with instrumentation among multiparous women.

QUESTION: Is there an association between induction of labor and cesarean section and induction of labor and vaginal birth with instrumentation among multiparous women?

METHODS: A population-based cohort study was conducted using Missouri Maternally Linked Cohort data from 1989 to 1997. The study sample included 49,915 second time mothers with singleton birth at 37-41 weeks gestation, without medical or obstetrical complications, or previous cesarean section. The primary exposure was induction of labor and outcomes were cesarean section and vaginal delivery with instrumentation. Multivariate logistic regression models were used to estimate the risk association using crude and adjusted odds ratios, controlling for characteristics related to induction of labor and cesarean section.

FINDINGS: Study observed a 31% (95%CI:1.14-1.50) and 45% (95%CI:1.34-1.57) increase in likelihood of cesarean section and vaginal birth with instrumentation, respectively, in women whose labors were induced compared to women whose labors were not. After adjusting for covariates the risk of cesarean section was 22% (95%CI:1.06-1.41) higher and the risk of vaginal birth with instrumentation was 35% (95%CI:1.24-1.46) higher in women whose labors were induced compared to women who were not induced. Induction of labor is associated with an increased risk of cesarean section and vaginal birth with instrumentation in multiparous women after controlling for covariates.