Effect of the “shoulder-up” bundle on the incidence of spontaneous perineal injury after vaginal delivery: comparison of 2 historic cohorts after propensity score matching

Abstract

Perineal injury following vaginal delivery represents a major cause of long-term maternal morbidity and its prevention is among the priorities of modern Obstetric practice. To investigate whether the systematic implementation of a bundle of maneuvers to prevent perineal injury (i.e. the "shoulder-up" bundle) may reduce the rate of spontaneous perineal tears in women delivering at a single tertiary maternity unit. Single-center retrospective intervention study including all vaginal deliveries between April 1st 2020 and March 31st 2022. On March 1st, 2021, a bundle focused on perineal injury prevention in vaginal deliveries has been implemented and introduced as a standard of care. The "shoulder-up" bundle includes the addition of a hands on technique for the delivery of the posterior shoulder which is slowly lifted up under the direct visualization of the perineal body, immediately after the disengagement of the anterior shoulder. The labor ward staff underwent a dedicated training to acquire expertise on the "shoulder-up" bundle. Little changes in terms of medical and midwifery staffing were recorded during the study period. The incidence of spontaneous 2nd or higher degree perineal tears was compared between the patients who gave birth prior to the clinical implementation of the bundle (Standard care Group) and those who were delivered following the implementation of the bundle (Shoulder-up Group). A 1:1 propensity score matching of the two groups was done for the variables that proved to be independently associated with the perineal outcome. From April 1st 2020 to March 31st 2022, 3671 patients had a vaginal birth at our tertiary care Unit (1786 in the Standard Care group and 1885 in the "Shoulder-up" group) and were enrolled in the study population. Of these 1191 (32.4%) experienced a spontaneous 2nd or higher degree perineal tear; at univariate analysis nulliparity (59.6% vs 39.1%, p<.001), higher gestational age at delivery (39.8 ± 1.28 vs 39.4 ± 1.97 weeks, p<.001), epidural analgesia (40.6% vs 31.2%, p<.001), vacuum assisted delivery (9.6% vs 4.0%, p<.001) and birthweight > 4Kg (11.0% vs 6.3%, p<.001) resulted independently associated with the perineal outcome. Following propensity Score matching for the above cited factors, 1703 patients of either group were compared. A significant increase in the rate of intact perineum (71.0% vs 64.1%, p = 0.014) and a reduction in the incidence of 2nd (27.2% vs 32.9%, p = 0.006) and 3rd-4th degree perineal tears (1.3% vs 3.0%, p<.001) was demonstrated in the "shoulder-up" group. Among the subgroup of patients undergoing vacuum assisted delivery a borderline significant reduction in the OASIs rate (10.4% vs 2.9%, p=0.052) was also observed. Our study showed that the clinical implementation of the "shoulder-up" bundle at vaginal delivery is associated with a significant reduction in the incidence of spontaneous 2nd or higher degree perineal tears.