The association of vacuum-assisted delivery and shoulder dystocia among macrosomic newborns: a retrospective study.

Abstract

Although shoulder dystocia (ShD) is associated with fetal macrosomia and vacuum-assisted delivery (VAD), the independent role of the latter in the occurrence of ShD is yet to be completely elucidated, as it is difficult to study its true independent contribution to ShD formation in the presence of many confounding factors. Therefore, we aimed to study whether VAD is independently associated with an increased risk for ShD among macrosomic newborns. A retrospective cohort study from a single tertiary medical center including all women who delivered vaginally a macrosomic infant during 2011-2020. We allocated the study cohort into two groups: (1) VAD (2) spontaneous vaginal deliverys, and analyzed risk factors for ShD. A multivariate regression analysis was performed to identify determinants independently associated with ShD occurrence. Of 2,664 deliveries who met the study inclusion criteria, 118 (4.4%) were VAD. The rate of ShD in the entire cohort was 108/2664 (4.1%). The following factors were more frequent among the VAD group: no previous vaginal delivery [odds ratio (OR) 2.4 (95% confidence interval (CI) 1.4-4.0, p < 0.001)], prolonged second stage (OR 11.9; 95% CI 8.1-17.6, p < 0.01), induction of labor (OR 2.4; 95% CI 1.5-3.8, p < 0.01) and ShD (OR 2.0; 95% CI 1.0-4.1, p = 0.04). ShD was associated with higher rates of maternal height < 160cm (OR 2.0; 95% CI 1.3-3.1, p < 0.01), pregestational diabetes (OR 7.2; 95% CI 2.0-26.8, p = 0.01), hypertensive disorder (OR 2.6; 95% CI 1.1-6.2, p = 0.02) and higher birthweight (mean 4,124 vs. 4,167g, p < 0.01). On multivariate regression analysis, the following factors remained independently associated with ShD occurrence: increased birthweight (aOR 1.0; 95% CI 1.0-1.0, p < 0.01), pregestational diabetes (aOR 5.3; 95% CI 1.1-25.0, p = 0.03), while maternal height was negatively associated with ShD (aOR 0.9; 95% CI 0.9-0.9, p < 0.01). In deliveries of neonates above 4000g, VAD did not independently increase the risk of ShD occurrence. Therefore, when expeditious delivery of a macrosomic infant is required, VAD is a viable option.