Associations between maternal race, socioeconomic status and shoulder dystocia: a population-based retrospective cohort study in Ontario Canada

BACKGROUND: Shoulder dystocia is a severe and emergent adverse perinatal complication. Existing literature suggests that the risk of shoulder dystocia varies by race and socioeconomic status, but research in this area is lacking in Canada. OBJECTIVES: To examine variations of shoulder dystocia by maternal race and maternal socioeconomic status and evaluate the interaction between race and macrosomia on the occurrence of shoulder dystocia. STUDY DESIGN: We conducted a population-based retrospective cohort study including White and Black pregnant people who participated in prenatal screening and had singleton stillbirths or live hospital births, excluding those with no-labour caesarean deliveries, from January 1, 2013 to March 31, 2021 in Ontario, Canada. The BORN Information System and Canadian Institute for Health Information databases were linked for analysis. We used multivariable Poisson regression with robust error variance models to examine the association between maternal race, neighbourhood household median income and educational level, and shoulder dystocia, while adjusting for maternal age, parity, previous caesarean section, obesity, substance use, pre-existing physical and mental health conditions, gestational diabetes, obstetrician in antenatal care team, hospital level of maternal care, gestational age, infant sex and rural residence. The interaction between maternal race and fetal macrosomia on the outcome of shoulder dystocia was evaluated. RESULTS: Among the total cohort of 422,580 pregnant individuals, 10.2% were Black individuals and 89.8% were White individuals. The incidence of shoulder dystocia was 4.4% (N = 18,592) among the entire cohort, 4.4% (N = 16,739) among White individuals and 4.3% (N = 1,853) among Black individuals. There was a statistically significant interaction (P < 0.001) between maternal race and infant macrosomia on shoulder dystocia. Among the sub-cohort of pregnant individuals giving birth to infants with macrosomia, Black individuals had a 17% higher risk of experiencing shoulder dystocia (aRR: 1.17, 95% CI: 1.08–1.28) than White individuals. Individuals living in the lowest-income and least educated neighborhoods had a 19% and 25% higher risk of experiencing shoulder dystocia, respectively, compared to those in the wealthiest or most educated neighborhoods. However, no significant racial or household income differences on shoulder dystocia were observed among those giving birth to non-macrosomic infants. CONCLUSION: The higher risk of shoulder dystocia among birthing individuals in lower socioeconomic status neighborhoods, coupled with the elevated risk for Black individuals at the same socioeconomic status level, suggests a double burden faced by Black individuals under Ontario’s universal healthcare system. The relationships between race, socioeconomic status, and macrosomia in shoulder dystocia are complex, highlighting the need for further studies to investigate potential racial disparities and discrimination. There is a need for policies and interventions that specifically address these inequities among Black communities to improve healthcare in Ontario.