572: Predictors of shoulder dystocia at the time of operative vaginal delivery: A prospective population-based cohort study

Abstract

To identify factors associated with shoulder dystocia following an attempted operative vaginal delivery (aOVD) in a prospective population-based cohort study, evaluate whether these factors can be used to accurately predict shoulder dystocia, and build a predictive score for shoulder dystocia. This was a planned secondary analysis of data collected for a prospective population-based cohort study of 2,138 deliveries with aOVD et term from 2008-2013. Its design was to estimate severe maternal and neonatal morbidity after aOVD according to the fetal head station [mid- (391/2,138; 18.3%), low- (1,550/2,138; 72.5%), and outlet-pelvic (197/2,138; 9.2%)]. Cases were defined as women with a shoulder dystocia following aOVD (defined as a delivery that requires additional maneuvers for delivery of the fetal shoulders), and women without a shoulder dystocia were defined as controls. A risk score for shoulder dystocia following aOVD was derived using univariate and multivariate logistic regression analyses. Ability of the tool to predict shoulder dystocia was assessed using the area under the receiver operating characteristic curve (AUC). Shoulder dystocia occurred in 55 women (2.6%): 13 (3.3%) mid-, 39 (2.5%) low- and 3 (1.5%) outlet-pelvic aOVD (P=.34). Women with shoulder dystocia had more often a history of shoulder dystocia (P=.01), gestational age (GA)≥40 weeks (P=.03), and second stage longer than 3h (P=.03) in sub-group of midpelvic aOVD. In multivariable analysis, a history of shoulder dystocia was the only factor independently associated with shoulder dystocia following aOVD (aOR 27.00, 95%CI 4.10-178.00). No other statistical association was observed for the following predictors: age≥35 years, BMI≥35, height<160cm, multiparity, GDM, antenatal suspicion of macrosomia, GA≥41 weeks, induced labor, epidural analgesia, second stage longer than 3 h, and active phase of second stage longer than 30 min. The AUC was 0.65 (95% CI 0.57-0.73) (Fig. 1). Although our data are robust from a large, prospective population-based cohort study (carefully characterized obstetric patients, prospectively maintained database, carefully characterized neonates, and consistent rate of shoulder dystocia), risk factors identified before aOVD cannot be used to accurately predict a shoulder dystocia following aOVD.