Critical analysis of risk factors for shoulder dystocia

Objective The study was aimed to define trends, risk factors and perinatal outcome associated with shoulder dystocia (SD). Methods A population-based study comparing all singleton deliveries with and without SD was conducted. Statistical analysis was performed using multiple logistic regression analysis. Results Shoulder dystocia complicated 0.2% (n = 451) of all deliveries included in the study (n = 240,189). The rate of SD declined from 0.4% in 1988 to 0.13% in 2009. Independent risk factors for SD in a multivariable analysis were fetal macrosomia (birth-weight ≥ 4 kg; OR = 16.1; 95% CI 13.2-19.6, P<0.001), failure of labor to progress during the second stage (OR = 2.4; 95% CI 1.5-3.7, P<0.001), diabetes mellitus (OR = 1.8; 95% CI 1.4-2.3, P<0.001) and advanced maternal age (years, OR = 1.02; 95% CI 1.001-1.03, P = 0.029). Perinatal mortality was significantly higher after SD as compared to the comparison group (6.2 vs. 1.4%, P<0.001). Another multivariable analysis, with perinatal mortality as the outcome variable, controlling for confounders such as maternal age, gestational age, diabetes mellitus, etc. was constructed; SD was noted as an independent risk factor for perinatal mortality (adjusted OR = 11.1; 95% CI 7.2-17.1, P<0.001). Conclusions Shoulder dystocia, associated with macrosomia, labor dystocia, diabetes mellitus, and advanced maternal age, is an independent risk factor for perinatal mortality. In an era of increased rate of cesarean deliveries, and perhaps increased accuracy of birth weight estimation, the rate of shoulder dystocia gradually declines.