Objective: To investigate risk factors associated with postterm pregnancy and cesarean delivery following labor induction.
Design: Population-based cohort study.
Setting: Sweden.
Population: From the Swedish Medical Birth Register, a total of 1,176,131 singletons births from gestational week 37 and onwards, between 1992 and 2006.
Methods: Unconditional logistic regression analysis.
Main outcome measures: Risk of postterm pregnancy (delivery at >or=42 weeks) and cesarean delivery following labor induction.
Results: Among 1,176,131 births, 8.94% were delivered postterm. Compared to normal weight women, the risk of postterm pregnancy in obese women was almost doubled (adjusted OR: 1.63, 95% CI 1.59-1.67). The risk of postterm pregnancy increased with increasing maternal age and was higher among primiparous women. The risk of cesarean section (CS) following labor induction postterm, increased with maternal age and BMI, and was more than doubled among women 35 years and older (adjusted OR 2.28, 95% CI 2.04-2.56). A fivefold risk of CS was seen among nulliparous women (adjusted OR 5.05, 95% CI 4.71-5.42). Parous women with a previous CS undergoing labor induction had a sevenfold increased risk of CS postterm (adjusted OR 7.19, 95% CI 5.93-8.71).
Conclusions: Nulliparity, advanced maternal age and obesity were the strongest risk factors for postterm pregnancy and CS following labor induction in postterm pregnancy. Including maternal risk factors to the cervical assessment may improve prediction of vaginal delivery following labor induction in postterm pregnancy.