147 To pull or not to pull: clinical factors associated with failed operative vaginal delivery

While successful operative vaginal delivery (OVD) may reduce severe maternal morbidity (SMM) and severe neonatal morbidity (SNM), failed OVD may increase both, highlighting the importance of patient selection. We sought to identify traditional factors, such as macrosomia, and non-traditional factors, such as a maternal comorbidity composite, associated with failed OVD in a large U.S. cohort. We used a population-based database of linked patient discharge data and birth certificates to evaluate nulliparous, term, singleton, vertex livebirths after OVD attempt in California between 2007-2012. The primary outcome was successful OVD. Factors potentially associated with failed OVD were selected a priori, including maternal age, BMI, high birthweight as proxy for estimated fetal weight, labor induction, episiotomy, and obstetric comorbidity score (a validated composite). The relative risk of failed OVD was estimated using mixed-effects robust Poisson multivariable regression models (women nested within hospitals). Confounders were selected a priori using causal diagrams. Vacuum and forceps were evaluated separately in stratified analyses. Among 92,866 attempted OVDs, 93% were successful and 7% failed resulting in cesarean birth. Women who had a failed OVD were more likely to be obese and have a higher obstetric comorbidity score, among other characteristics (Table 1). Factors associated with failed OVD included high comorbidity score (≥5; aRR 2.58, 95% CI 2.15-3.10), and birthweight >4000g (aRR 2.39, 95% CI 2.17-2.64); macrosomia was more strongly associated with failed vacuum (aRR 2.88, 95% CI 2.60-3.19) than failed forceps (aRR 1.62, 95% CI 1.23-2.14, Table 2). In contrast, episiotomy (aRR 0.48, 95% CI 0.29-0.79) was associated with a reduced risk of failed OVD. We identified several unique clinical factors, such as maternal comorbidities and episiotomy, to consider when attempting an OVD. Incorporating these additional components into decision making might improve OVD success rates.View Large Image Figure ViewerDownload Hi-res image Download (PPT)