Introduction
Obstetric Anal Sphincter Injury (OASI) is the commonest cause of anal incontinence (AI) affecting young women. The incidence of OASI in primiparous women tripled to 5.9% in the UK between 2000-2012 (1) equating to 3,500 women in the UK annually. AI is defined as the involuntary loss of solid or liquid stool and or flatus. Women with OASI are between two to three times more likely to develop AI than women having an uncomplicated vaginal birth (2). Specific risk factors for AI include parity, degree of OASI and age (as risk of AI increases over a woman’s lifetime) (3). Women who have recurrent OASI and fourth degree tears are particularly affected by more frequent and severe long-term symptoms of AI (4, 5). At least 10% of women who are initially asymptomatic after OASI become symptomatic by three years (6).
The presence of AI is the most important determiner of women’s quality of life (QOL) after OASI (7). The ’OASIS syndrome’ has been described in a study of women with AI after OASI. Feelings include being unclean, isolation, grief, anxiety, a feeling of mutilation, loss of dignity, guilt and a negative effect on motherhood, sexual intimacy and partner relations (8). Women with OASI have worse longer-term quality of life outcomes than women without OASI; this significantly correlates with symptoms of AI and number of OASI births (9). All symptoms of AI can be profoundly upsetting to women; Jango et al demonstrated a Wexner score ≥2 sufficient to affect quality of life in the long-term after OASI (10).
In women who deliver again after OASI, incidence of AI is particularly high; 48% by 2-5 years in one study (11). The long-term incidence of AI was 58.8% after a fourth-degree tear and 41.0% after a third-degree tear at a median of 8.5 years after a second birth in a population-based study (12). Additional risk factors in these women include pre-existing symptoms of AI, either ‘transient AI’ (13) or ‘permanent AI’ (2) after index birth. AI is therefore of vital consideration for all women choosing their mode of birth in subsequent pregnancies after OASI. Based on expert opinion, the Royal College of Obstetricians and Gynaecologists (RCOG) recommends medical discussion regarding birth options for symptomatic women or those with abnormal endoanal ultrasonography and/or manometry. The American College of Obstetricians and Gynaecologists (ACOG) recommend offering a cesarean section (CS) to women experiencing either AI or perineal breakdown after birth.
Birth choice is personal and can be emotive. There is a wide variation in practice between units including access to specialist perineal clinics and use and interpretation of anorectal investigations including endoanal ultrasound (EAUS) and anorectal manometry (ARMS). A 2014 survey of UK women demonstrated that only one third had access to a perineal clinic, and less than one fifth had access to endoanal ultrasound after OASI (14). Protocols outlining interpretation of anorectal investigations to directivity counsel women on planned mode of birth (MOB) after OASI differ between units (11, 15, 16, 17, 18, 19). Evidence suggests that the majority of women in the UK are counselled regarding subsequent MOB based on their symptoms and preferences alone (14).
This study aims to systematically review and meta-analyse current evidence to determine whether CS is protective against the development of AI after OASI.