Poster session II Diabetes, labor, medical-surgical-disease, obstetric quality & safety, prematurity, ultrasound-imaging: Abstracts 237 – 386| Volume 206, ISSUE 1, SUPPLEMENT , S145, January 01, 2012

302: Term induction of labor: a possible cause for subsequent preterm birth?


      It is estimated that >20% of women undergo induction of labor (IOL), and this continues to rise. Simultaneously, the preterm birth (PTB) rate remains largely unchanged. Previously published work from our institution demonstrates the rate of spontaneous PTB (SPTB) in women with a prior term delivery is 5.7%, which is lower than the national average (Edlow et al. AJOG 2007). The objectives of this study were to 1) determine the rate of SPTB in a subsequent pregnancy among women who previously underwent a term IOL and 2) evaluate the association between different methods of term IOL on subsequent SPTB risk.

      Study Design

      A retrospective cohort study of women with 2 deliveries (a term IOL and a subsequent delivery) between 2005 & 2010 at the Hospital of the University of Pennsylvania was performed. Maternal medical, obstetrical, and delivery information for both pregnancies were obtained through chart abstraction. The rate of SPTB among pregnancies following term IOL was calculated. Associations between methods of IOL and SPTB rate were calculated using χ2analyses or fishers exact tests.


      The study included 413 women. For method of IOL, 94 (23%) had a cervical foley, 172 (42%) had only prostaglandin, and 147 (36%) had only pitocin. The overall SPTB rate among subsequent pregnancies after term IOL was 7.5%. The rate of SPTB when cervical foley was used vs. medical IOL agents was 9.6% vs. 6.9% (RR 1.39[0.66-2.91], p=0.39). When analyses were restricted to women whose first pregnancy was a term IOL (N=278), the SPTB rate in subsequent pregnancies was 6.5%. Among these women, the SPTB rates were 8.9% vs. 5.5% (RR 1.60[0.64-3.99], p=0.31) for those who had a cervical foley vs. medical IOL agents respectively.


      The observed SPTB rate of 7.5% in women who had a term IOL is higher than the previously published 5.7%. Interestingly, the risk is differentially increased when comparing mechanical vs. medical IOL agents. Further research is needed to evaluate the impact of IOL and methods of IOL on subsequent PTB risk in order to ensure the increasing IOL rate is not causing unnecessary harm.