Predicting Spontaneous Labor beyond 39 Weeks among Low-Risk Expectantly Managed Pregnant Patients

Abstract

Objectives: To identify characteristics associated with spontaneous labor onset in pregnant patients undergoing expectant management at greater than 39 weeks’ gestation and delineate perinatal outcomes associated with spontaneous labor compared with labor induction. Study design: This was a retrospective cohort study of singleton pregnancies ≥390/7 weeks gestation delivered at a single center in 2013. Exclusion criteria were elective induction, cesarean delivery or presence of a medical indication for delivery at 39weeks, more than one prior cesarean delivery, fetal anomaly or demise. We evaluated prenatally available maternal characteristics as potential predictors of the primary outcome-spontaneous labor onset. Multivariable logistic regression was used to generate two parsimonious models – one with and one without third trimester cervical dilation. We also performed sensitivity analysis by parity and timing of cervical examination, and compared mode of delivery and other secondary outcomes between patients who spontaneous labored and those who did not. Results: Of 707 eligible patients, 536(75.8%) attained spontaneous labor and 171(24.2%) did not. In the first model, maternal BMI, parity and substance use were identified as the most predictive factors. Overall, the model did not predict spontaneous labor(AUC 0.65, 95% CI 0.61-0.70) with high accuracy. The addition of third trimester cervical dilation in the second model did not significantly improve labor prediction(AUC 0.66, 95% CI: 0.61-0.70; p=0.76). These results did not differ by timing of cervical examination or parity. Patients admitted in spontaneous labor had lower odds of cesarean delivery(OR 0.33, 95% CI 0.21-0.53) and NICU admission(OR 0.38, 95% CI 0.15-0.94). Other perinatal outcomes were similar between groups. Conclusions : Maternal characteristics did not predict spontaneous labor onset ≥39 weeks’ gestation with high accuracy. Patients should be counseled on challenges of labor prediction regardless of parity and cervical examination, outcomes if spontaneous labor does not occur and benefits of elective labor induction discussed.