571: Predictors of failed operative vaginal delivery: A prospective population-based cohort study

Abstract

To identify factors associated with failed attempted OVD (aOVD) in a prospective population-based cohort study, evaluate whether these factors can be used to accurately predict failed OVD, and build a predictive score for failed aOVD. This was a planned secondary analysis of data collected for a prospective population-based cohort study of 2,138 deliveries with an aOVD at term from 2008-2013. Its design was to estimate severe composite 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%)]. Women in the case group were defined as women who had aOVD but required ultimately cesarean delivery, and women who delivered vaginally after aOVD were defined as controls. A risk score for failed aOVD was derived using univariate and multivariate logistic regression analyses. Ability of the tool to predict failed aOVD was assessed using the area under the receiver operating characteristic curve (AUC). Failed aOVD occurred in 39 women (1.8%): 35 (8.9%) mid-, and 4 (0.3%) low-pelvic aOVD (P<.0001). Women with failed aOVD had more often gestational age (GA)≥40 weeks (P=.003), fetal occiput-posterior position (P<.0001), mid station at application (P<.0001), aOVD performed by senior obstetrician (P<.0001), vacuum (P<.0001), and less often with active phase of second stage longer than 30 min (P=.005). Failed aOVD was associated with severe maternal morbidity (P=.0008) without increasing risk of severe neonatal morbidity (P=.07). The risk score for failed aOVD included the following predictors: vacuum (+1), fetal occiput-posterior position (+1), and aOVD for arrested progress (+1), active phase of second stage longer than 30 min (-1), GA≥40 weeks with midpelvic aOVD (+1). The AUC was 0.83 (95% CI 0.75-0.91) (Fig.1). A cut-off point of 2 had Se of 66.7%, Sp of 93.6%, and PPV of 93.2% for cesarean delivery after failed aOVD. If failed aOVD was considered as women who had aOVD but required sequential use of 2 instruments or ultimately cesarean delivery (n=117; 5.5%), the AUC was 0.77 (95%CI 0.73-0.80) (Fig.2). Using a cut-off point of 2, failed aOVD was predicted with Se, Sp, and PPV of 35.3%, 94.2%, and 90.9%, respectively. Risk factors identified before an aOVD should be easily used to accurately predict whether an aOVD will fail.View Large Image Figure ViewerDownload Hi-res image Download (PPT)