Risk factors and fetal outcome in cases of shoulder dystocia compared with normal deliveries of a similar birthweight

Objectives To compare risk factors and fetal morbidity in deliveries complicated by shoulder dystocia with deliveries of similar infant birthweights but not complicated by shoulder dystocia. Design A retrospective case-controlled study. Setting Kuwait Maternity Hospital. Participants Sixty-nine cases of true shoulder dystocia and 138 controls matched for exact infant's birthweight. Methods Demographic data and data regarding history of previous shoulder dystocia, diabetes mellitus, labour course, method of delivery and newborns' condition were collected from patients and case notes following delivery. The mothers' height and weight were measured. Oral glucose tolerance test were performed on patients who were not known as diabetics. The infants' head and chest circumferences and bisacromial diameter were measured. Results There were no significant differences between cases and controls when mean age, parity, height, weight and gestational ages were compared. The cases demonstrated a higher incidence of previous shoulder dystocia (P < 0.01), diabetes mellitus (P < 0.001), use of oxytocin for acceleration of labour (P < 0.01) and operative vaginal deliveries (P < 0.01). Differences between cases and controls in their newborn infants' head and chest circumferences were not significant, but the newborns of cases have a longer mean bisacromial diameter and a shorter head circumference:bisacromial diameter ratio (P < 0.001 and P < 0.001, respectively). Thirty-seven infants (53.6%) from cases and two from controls (1.4%) sustained birth injuries. There were two stillbirths among the cases. Conclusions Although fetal macrosomia is the principal risk factor for shoulder dystocia, other important risk factors include diabetes mellitus, previous history of shoulder dystocia, prolonged labour, delay in the second stage of labour and fetal shoulder width which appear to be independent of fetal weight.