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Objectives. - To assess whether pelvic size and shape, spinal curvature, perinea] body length and genital hiatus size are associated with the incidence of childbirth pelvic floor trauma. Special situations, such as obesity, ethnicity and hyperlaxity, will also be studied.

Methods. - A bibliographic research using Pubmed and Cochrane Library databases was conducted until May 2018. Publications in English and French were selected by initial reading of the abstracts. Randomized trials, meta-analyzes, case-control studies and large cohorts were studied in a privileged way.

Results. - A pubic arch angle < 90 degrees (measured clinically) does not appear to increase the risk of OASIS (Level 3), but appears to be a risk factor for postnatal anal incontinence at short-term, but not at long-term (Level 3). Measurement of pelvic dimensions and the subpubic angle is not recommended to predict OASIS or to choose the mode of delivery for the purpose of protecting the perineum (Grade C). Prenatal measurement of both perineal body (Level 3) and genital hiatus (Level 2) does not predict the incidence of 2nd or 3rd degree OASIS. Therefore, the routine prenatal measurement of the length of the perineal body or the genital hiatus is not recommended for any objective related to perineal protection (Grade C). Levator avulsion, resulting in a widening of the genital hiatus, is potentially a source of long-term pelvic floor dysfunction. Biomechanical models suggest that performing a mediolateral episiotomy and applying the fingers to the posterior perineum at the time of expulsive phase may reduce pelvic floor trauma. Obese women have a longer perineal body (Level 3), and obesity does not seem to increase the risk of OASIS (Level 2). There is no difference between Asian and non-Asian women perineal body (Level 3). No studies have validated that the liberal practice of episiotomy in Asian women reduced the risk of OASIS. It is therefore not recommended to practice an episiotomy for simple ethnic reasons in Asian women (Grade C). Compared to white women, black women do not appear to have an increased risk of OASIS and even appear to have a decreased risk of perineal tears of all stages (Level 2). Ligament hyperlaxity seems to be associated with an increased risk of OASIS (Level 2).

Conclusions. - Prenatal assessment of pelvis bone, spine curvature, perineal body and genital hiatus do not allow to predict the incidence of childbirth pelvic floor trauma. Obesity and ethnicity are not risk factors for OASIS. (C) 2018 Elsevier Masson SAS. All rights reserved.