What are the factors that may predict the severity of perineal tears in obstetric anal sphincter injuries and how are their outcomes? A 10-year retrospective analysis in a Southeast Asian population.

Introduction And Hypothesis: Obstetric anal sphincter injuries (OASIS) complicate around 1-2% of deliveries in low- and middle-income countries. Asians are twice more likely to suffer this complication. The 3c and 4th-degree perineal tears that involve the internal anal sphincter muscle and the anal mucosa have been reported to have a poorer outcome and higher risk of recurrence compared to less severe tears.

Methodology: A retrospective 10-year analysis of third- and fourth-degree perineal tears in a tertiary centre was conducted. The maternal, neonatal factors and their respective outcomes after the repair of an OASI were examined and compared between minor (3a and 3b perineal tears) and major anal sphincter tears (3c and 4th-degree perineal tears).

Results: Five hundred twenty patients with OASIS were included into the study. Birthweight ≥ 3.5 kg was significantly associated with having a major anal sphincter tear in this study population, OR 1.91 (95% CI 1.21-3.02), p = 0.006. There was no significant difference in having faecal or flatus incontinence after the repair; however, major anal sphincter tears appeared to be more complicated to repair compared to minor anal sphincter tears, requiring involvement of the consultant, p < 0.001.

Conclusion: Neonatal birthweight ≥ 3.5 kg was the most significant factor in predicting the severity of OASIS in this study population. After appropriate repair, the rates of reported complications appeared similar between the two groups. However, significantly more expertise and resources were required for the repair of higher degree OASIS.