Women with gestational diabetes mellitus in the ACHOIS trial: risk factors for shoulder dystocia.

BACKGROUND Gestational diabetes mellitus (GDM) is associated with increased risk of fetal macrosomia and shoulder dystocia. However, not all women with GDM and fetal macrosomia have shoulder dystocia. AIMS To identify the risk factors for shoulder dystocia in women with gestational diabetes using data from women recruited into the routine care group of the ACHOIS trial. METHODS A secondary analysis was performed on data collected from women enrolled in the ACHOIS trial. Bivariate analyses were performed using the Fisher exact test. Variables found to be significantly associated with shoulder dystocia and previously identified risk factors were used as explanatory variables in multivariate analyses. RESULTS A positive relationship was found between the severity of maternal fasting hyperglycaemia and the risk of shoulder dystocia, with a 1 mmol increase in fasting oral glucose-tolerance test leading to a relative risk (RR) of 2.09 (95% CI 1.03-4.25). Shoulder dystocia occurred more often in births requiring operative vaginal delivery (RR 9.58, 95% CI 3.70-24.81, P < 0.001). Macrosomic and large-for-gestational-age infants were more likely to have births complicated by shoulder dystocia (RR 6.27, 95% CI 2.33-16.88, P < 0.001 and RR 4.57, 95% CI 1.74-12.01, P < 0.005, respectively). Fetal macrosomia was the only variable to maintain its significance in all multivariate analyses. CONCLUSIONS Fetal macrosomia is the strongest independent risk factor for shoulder dystocia. Effective preventative strategies are needed.