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.