Beyond the numbers: Impact of obesity on obstetric anal sphincter injury (OASI) outcomes in women

Objective: To compare the risk profiles, anatomical, and functional outcomes between obese and non-obese women who experienced obstetric anal sphincter injury (OASI). Methods: A retrospective electronic database study was conducted at Cork University Maternity Hospital (CUMH). Women with missing data/repairs conducted outside CUMH were excluded. Participants were categorized into obese (BMI ≥30 kg/m²) and non-obese (BMI <30 kg/m²) groups. Primary measure was a composite adverse outcome assessed 6 months post-delivery, including one or more of the following: resting pressure <40 mmHg, squeezing pressure <100 mmHg, defects in the internal and/or external anal sphincter. Statistical analyses were performed using SPSS version 28. Results: Among the 349 women included in the study, 285 (81.7%) had a BMI <30 kg/m² and 64 (18.3%) had a BMI ≥30 kg/m². Gestational diabetes was significantly higher in obese women. No significant differences were observed in newborn weight or mode of delivery. The majority of tears were classified as grade 3B in both groups. Attendance rates at the OASI clinic did not differ between the groups. Among those attending, no statistical differences were noted in manometry results, which were reduced in both groups. Rates of internal anal sphincter defects were lower in the obese group (7.0% vs 15.6%, P = 0.15) and external anal sphincter defects were significantly lower in obese women (0% vs 9.1%, P = 0.04). No difference was found in the rates of composite adverse outcomes between the groups. Conclusion: Functional outcomes and manometry results did not differ, but non-obese women had higher rates of anatomical defects in OASI, requiring further study.