Obstetric anal sphincter injury in the second birth after perineal wound complication in the first birth: A nationwide register cohort study

ObjectiveTo investigate whether perineal wound complications in the first birth, alone or in conjunction with obstetric anal sphincter injury (OASI), is associated with an increased risk of OASI in the second birth.DesignNationwide population-based cohort study.SettingSweden.PopulationWomen (n = 411 317) with first and second singleton vaginal births in Sweden, 2001-2019.MethodsData on diagnostic codes and surgical procedures were retrieved from the Swedish Medical Birth Register and the Swedish Patient Register. A perineal wound complication was defined as wound infection, dehiscence or perineal haematoma within 2 months of childbirth.Main outcome measuresAssociations between wound complications in the first birth and OASI in the second birth were investigated with logistic regression and presented as adjusted odds ratios (aORs) with 95% confidence intervals (95% CIs).ResultsIn total, 2619 (0.6%) women had a wound complication in the first birth, and 5318 (1.3%) had an OASI in the second birth. Women with a wound complication but no OASI in the first birth had more than doubled odds of OASI in the second birth (aOR 2.73, 95% CI 2.11-3.53). Women with OASI and a wound complication in the first birth had almost tenfold odds (aOR 9.97, 95% CI 6.53-15.24) of recurrent OASI.ConclusionsPerineal wound complication in the first birth increases the likelihood of OASI in a subsequent birth.