The Effect of Primary Delivery of the Anterior Compared With the Posterior Shoulder on Perineal Trauma: a Randomized Controlled Trial

Background Approximately 85% of vaginal deliveries are accompanied by trauma to the genital tract, with a higher risk at the first compared to subsequent vaginal births [1,2]. Among primipara with vaginal deliveries, 86% sustain a vaginal or perineal tear, and 77% require suturing of a lesion [1,3].

Birth trauma is associated with both short- and long-term morbidity, including pain, discomfort, dyspareunia, and fecal incontinence, and perineal trauma may cause social problems and affect the psychological well-being of the mother [1,4]. The level of postpartum morbidity is related to the degree of trauma [5,6], and studies of preventive measures are therefore of interest.

Genital tract traumas are classified into subtypes according to the location and severity of the lesion. Most studies have evaluated the risk factors for 3rd- and 4th-degree perineal tears that include the anal sphincter complex, the so-called obstetric anal sphincter injuries (OASIS). Predisposing factors are increasing maternal age, heavier birthweight, longer duration of the second stage of labour, oxytocin augmentation, occiput posterior position, and instrumental delivery [7-9]. The risk increases with the number of different risk factors [9]. Protective factors are previous vaginal delivery, epidural analgesia, and multiparity [7-9]. Several perineal management techniques used during delivery have been studied, and a recent Cochrane review concluded that warm compresses and perineal massage seem to reduce the risk of OASIS [4]. The introduction of an interventional perineal protection programme also seems to reduce the incidence of OASIS [10-12].

Leading textbooks recommend primary delivery of the anterior shoulder by gentle traction if the shoulders are not delivered spontaneously [13,14]. However, if shoulder dystocia occurs, the recommended manoeuvres are primary delivery of the posterior arm or primary delivery of the posterior shoulder, with the woman positioned on her hands and knees (Gaskin's manoeuvre) [15,16]. A computer-simulated trial of the manoeuvres used during shoulder dystocia found that primary delivery of the posterior arm caused an 80% reduction in the delivery force and a 70% reduction in stretch to the brachial plexus [17]. Primary delivery of the posterior shoulder could therefore be of advantage during uncomplicated deliveries, but, to the knowledge of the authors, various methods of shoulder delivery have never been studied previously.

The objective of this trial is to evaluate the incidence and degree of perineal trauma after primary delivery of the anterior shoulder compared to primary delivery of the posterior shoulder during vaginal birth in primiparous women in a randomized controlled trial. The hypothesis is that primary delivery of the posterior shoulder reduces the rate and degree of perineal trauma.