Postdates induction with an unfavorable cervix and risk of cesarean

Objective: To determine the risk of cesarean delivery associated with postdates induction (>= 41weeks) compared to term induction (37-40w6d) among women with an unfavorable cervix, and to examine the risk factors associated with cesarean among women undergoing postdates induction.Methods: A planned secondary analysis of a large prospective cohort study on induction (n=854) was performed. Women with a singleton gestation, intact membranes, and an unfavorable cervix (Bishop score of <= 6 and dilation <= 2cm) who were undergoing a term (>= 37weeks) induction for any indication were included. Women with a prior cesarean were excluded. The primary outcome was cesarean delivery. Relative risk of cesarean was estimated using a modified Poisson's regression model.Results: There was a significantly increased risk of cesarean for women undergoing postdates induction (n=154) compared to women 37-40w6d (n=700), (46.8 versus 26.0%, p<.001). This increased risk of cesarean remained after adjustment for race, parity, and pregnancy-related hypertension (aRR 1.70 [1.39-2.09], p<.001). Risk factors independently associated with cesarean among women >= 41weeks included nulliparity (aRR 3.38 95%CI (2.42-4.74)), BMI >= 30 (aRR 1.72 95%CI (1.34-2.21)), and starting cervical dilation <1cm (aRR 1.37 95%CI (1.11-1.70)).Conclusions: Women >= 41weeks undergoing an induction with an unfavorable cervix are at a significantly increased risk of cesarean compared to women 37-40w6d, with nulliparity, obesity, and cervical dilation <1cm being independent risk factors. These data can be used to augment patient counseling and support the ongoing discussion regarding the risk of post dates induction.