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.