Incidence trends of shoulder dystocia and associated risk factors: A nationwide analysis in the United States

ObjectiveTo examine recent incidence trends and characteristics of shoulder dystocia. MethodsThis is a retrospective cohort study querying the Healthcare Cost and Utilization Project's National Inpatient Sample. The study population included 9 913 838 vaginal deliveries for national estimates from January 2016 to December 2019. The main outcome measure was the diagnosis of shoulder dystocia. A binary logistic regression model was used to identify characteristics of shoulder dystocia in multivariable analysis. ResultsShoulder dystocia was reported in 228 120 deliveries (23.0 per 1000). The incidence of shoulder dystocia increased from 21.0 to 24.6 per 1000 deliveries during the 4-year study period (17.1% relative increase, P < 0.001). In a multivariable analysis, the recent year of delivery remained an independent factor for shoulder dystocia: adjusted odds ratio (aOR) compared with 2016, 1.09 (95% confidence interval [CI], 1.08-1.11), 1.13 (95% CI, 1.12-1.14), and 1.18 (95% CI, 1.16-1.19) for 2017, 2018, and 2019, respectively. Large for gestational age (aOR 4.33 [95% CI, 4.25-4.40]), diabetes mellitus (pregestational aOR, 4.78 [95% CI, 4.63-4.94], and gestational aOR, 1.69 [95% CI, 1.66-1.71]), and vacuum-assisted delivery (aOR, 2.18 [95% CI, 2.15-2.21]) exhibited the largest risks for shoulder dystocia. ConclusionThis national-level analysis identified various risk factors for shoulder dystocia and demonstrated that shouder dystocia cases are increasing gradually in the United States.