Levator ani muscle is one of the main components of perineal muscles and plays a crucial role in urinary continence and pelvic organ support. An avulsion, detachment from its insertion, of this muscle can occur during vaginal birth. It is well known that this major injury can cause many symptoms such as urinary incontinence and pelvic organ prolapses. Some risk factors of this important injury have been identified in the literature, such as the use of forceps. However, to date, no study has evaluated the impact of the crowning of the fetal head during labor on perineal muscles, specifically the levator ani muscle avulsion. Hence, the objectives of this study are to evaluate the association i) the time of the crowning of the fetal head during labor and levator ani muscle avulsion, ii) the time of the crowning of the fetal head and urogynecological symptoms, and iii) use of episiotomy and levator ani muscle avulsion. Postpartum primiparous women will undergo a 4D transperineal ultrasound to evaluate their pelvic muscles and complete questionnaires assessing urogynecological symptoms.

This is a prospective cohort study evaluating the impact of the crowning time of the fetal head in the second stage of labor on the incidence of levator ani muscle avulsion. Levator ani muscle is hypothesized to avulse during the distension of the pelvic floor muscles, as during a forceps use, and most probably during the crowning of the fetal head. In the study center, the crowning of the fetal head is systematically calculated during labor by nurses and doctors. To eliminate some potential confounding factors, only primiparous women with spontaneous vaginal delivery of a vertex position baby will be recruited in the post-partum period. In order to evaluate the presence of levator ani muscle avulsion, they will be assessed with a 4D transperineal ultrasound by using a standard diagnosis protocol. The delivery hospital file will then be examined to collect potential confounding variables. Prior to data collection, all study participants will give their written informed consent. This study will add more literature to the prevention of the levator ani muscle avulsion and its long-term complications.

Inclusion Criteria:

Primiparous women GxT1 At term: ≥ 37+0 weeks of gestation (included) Spontaneous vaginal delivery (SVD) Cephalic presentation History of miscarriage before 20 weeks or with a fetal weight < 350g

Exclusion Criteria:

Contraindications to vaginal delivery Assisted vaginal delivery Age under 18 years Shoulder dystocia Extensive pelvic reconstructive surgery (e.g., bladder exstrophy repair) Term intrauterine fetal demise Twin or multifetal pregnancy

The target population will recruit primiparous postpartum women who meet the inclusion criteria and gave birth at CHUS Fleurimont during the recruitment period.

Deidentified data will be made available upon approval by the principal investigator and study team.