[Definition, epidemiology and risk factors of obstetric anal sphincter injuries: CNGOF Perineal Prevention and Protection in Obstetrics Guidelines]

Objectives: The aim of this review was to agree on a definition of the obstetric anal sphincter injuries (OASIS), to determine the prevalence and risk factors.

Methods: A comprehensive review of the literature on the obstetric anal sphincter injuries (OASIS), establishment of levels of evidence (NP), and grades of recommendation according to the methodology of the recommendations for clinical practice.

Results: To classify obstetric anal sphincter injuries (OASIS), we have used the WHO-RCOG classification, which lists 4 degrees of severity. To designate obstetric anal sphincter injuries, we have used the acronym OASIS, rather than the standard French terms of "complete perineum" and "complicated complete perineum". OASIS with only isolated involvement of the EAS (3a and 3b) appears to have a better functional prognosis than OASIS affecting the IAS or the anorectal mucosa (3c and 4) (LE3). The prevalence of women with ano-rectal symptoms increases with the severity of the OASIS (LE3). In the long term, 35-60% of women who had an OASIS have anal or fecal incontinence (LE3). The prevalence of an OASI in the general population is between 0.25 to 6%. The prevalence of OASIS in primiparous women is between 1.4 and 16% and thus, should be considered more important than among the multiparous women (0.4 to 2.7%). In women with a history of previous OASIS, the risk of occurrence is higher and varies between 5.1 and 10.7% following childbirth. The priority in this context remains the training of childbirth professionals (midwives and obstetricians) to detect these injuries in the delivery room, immediately after the birth. The training and awareness of these practitioners of OASIS diagnosis improves its detection in the delivery room (LE2). Professional experience is associated with better detection of OASIS (LE3) (4). Continuing professional education of obstetrics professionals in the diagnosis and repair of OASIS must be encouraged (Grade C). In the case of second-degree perineal tear, the use of ultrasound in the delivery room improves the diagnosis of OASIS (LE2). Ultrasound decreases the prevalence of symptoms of severe anal incontinence at 1 year (LE2). The diagnosis of OASIS is improved by the use of endo-anal ultrasonography in post-partum (72h-6weeks) (LE2). The principal factors associated with OASIS are nulliparity and instrumental (vaginal operative) delivery; the others are advanced maternal age, history of OASIS, macrosomia, midline episiotomy, posterior cephalic positions, and long labour (LE2). The presence of a perianal lesion (perianal fissure, or anorectal or rectovaginal fistula) is associated with an increased risk of 4th degree lacerations (LE3). Crohn's disease without perianal involvement is not associated with an excess risk of OASIS (LE3). For women with type III genital mutilation, deinfibulation before delivery is associated with a reduction in the risk of OASIS (LE3); in this situation, deinfibulation is recommended before delivery (grade C).

Conclusion: It is necessary to use a consensus definition of the OASIS to be able to better detect and treat them.