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

Objective: To examine recent incidence trends and characteristics of shoulder dystocia.

Methods: This 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.

Results: Shoulder 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.

Conclusion: This national-level analysis identified various risk factors for shoulder dystocia and demonstrated that shouder dystocia cases are increasing gradually in the United States.