Shoulder dystocia and associated manoeuvres as risk factors for perineal trauma

Shoulder dystocia (SD) is an obstetric emergency that can be associated with serious neonatal morbidity and mortality. The aim of this study was to identify the incidence and risk factors for obstetric anal sphincter injuries (OASIS) in women who sustained SD at birth.

This was a retrospective observational study over a 5-year period whereby 403 cases of SD were identified. The primary outcome measure was to identify the incidence of OASIS in women with SD. We also evaluated the role of the manoeuvres used for the management of SD and aimed to identify possible correlations between specific manoeuvres and OASIS by univariate and multivariate regression analysis.

Shoulder dystocia was associated with a three-fold increase in the risk of OASIS in our population. The use of internal manoeuvres (OR 2.182: 95 % CI 1.173-4.059), an increased number of manoeuvres ≥ 4 (OR 4.667: 95 % CI 1.846-11.795), Woods' screw manoeuvre (OR 3.096: 95 % CI 1.554-6.169), reverse Woods' screw manoeuvre (OR 4.848: 95 % CI 1.647-14.277) and removal of the posterior arm (OR 2.222: 95 % CI 1.117-4.421) were all associated with a significant increase in the likelihood of OASIS.

In our study, instrumental deliveries, the use of internal manoeuvres (Woods' screw and reverse Woods' screw) and four or more manoeuvres for the management of SD were independently associated with a higher incidence of OASIS. To effectively manage shoulder dystocia with lower risks of perineal trauma, these factors could be considered when designing further prospective studies and developing management protocols.