Maternal pre-pregnancy body mass index and obstetric anal sphincter injury: A systematic review and meta-analysis.

Abstract

The relationship between pre-pregnancy body mass index (BMI) and obstetric anal sphincter injury (OASI) is not well established. OASI is a major obstetric complication, contributing to postpartum morbidity through chronic pain, anal incontinence, and impaired quality of life. To quantify the association of pre-pregnancy BMI on the risk of OASI. We searched seven databases (MEDLINE, OVID, Embase, Emcare, Cochrane Library, Wiley, and Web of Science) from inception to September 1, 2024, with an initial search performed on February 2, 2023 and an updated search conducted on September 1, 2024. Observational studies comparing the risk of OASI by pre-pregnancy BMI categories as specified by the World Health Organization (underweight, standard weight, overweight, obesity class I, obesity class II, and obesity class III) were included. Two reviewers independently completed screening, data extraction, and quality assessment of all included studies. Odds ratios (ORs) of included studies were pooled using random effects models. The quality of studies was assessed using Cochrane's ROBINS-E tool. Seven cohort studies fulfilled eligibility criteria for inclusion in the meta-analysis. Meta-analyses of adjusted estimates showed increased odds of OASI among individuals with underweight versus standard pre-pregnancy BMI (OR 1.29, 95% confidence interval [CI] 1.23-1.36), and lower odds of OASI were found in both the overweight (OR 0.94, 95% CI 0.89-0.99) and obese versus standard BMI (OR 0.80, 95% CI 0.73-0.88) groups. Heterogeneity among studies was moderate to high. Most studies were found to be at high risk of residual confounding. Maternal pre-pregnancy BMI is inversely associated with OASI in a dose-responsive manner, such that OASI risk decreases as BMI increases. These findings highlight the need to consider maternal BMI in risk stratification and preventative strategies during childbirth.