Objectives: This thesis aimed to assess the impact of maternal body mass index (BMI) on pelvic floor during labor and focusing on pelvic floor function following an anal sphincter injury (OASI). Additionally, the objective was to design a study protocol for a randomized controlled trial (RCT) with the objective to evaluate the impact of supplementary anesthesia during the examination and repair of obstetric perineal lacerations.

Material and Methods: Study I was an observational prospective cohort study, conducted at the maternity ward Linköping University Hospital, including 207 primiparous women in the active phase of labor. Transperineal ultrasound was used for measurement of the anovaginal distance (AVD) during active phase of labor, with AVD measurements analyzed in relation to the women's BMI groups. Study II and III were nationwide Swedish register studies, including 6595 women with a first time vaginal birth complicated by an OASI. Data was sourced from the Swedish Perineal Laceration Register (PLR), based on medical records and patient reported outcome measurements (PROM). Women were categorized by BMI, and analyses were performed on PROM data at the 8 week follow-up (Study II), and at the 12 month follow-up (Study III), after an OASI. Study IV, a study protocol for a RCT, with parallel groups. Women who undergo examination and repair of obstetric perineal lacerations (grade I and II) are randomized into two arms (1:1); analgesia with pudendal nerve block (PNB) with Ropivacaine®-the PNB group or analgesia with PNB in combination with patient-controlled sedation (PCS) with propofol, the PCS group.

Results: Obese women exhibited a higher AVD compared to normal weight women. The mean AVD was 25 mm for primiparous women in the active phase of labor. Overweight and obese women reported fewer wound complications than normal weight women at 8 weeks postpartum. Additionally, overweight and obese women had a lower risk of anal incontinence (AI) at 8 weeks after an OASI compared to normal weight counterparts. However, at 12 months after an OASI, the risk of AI was comparable across BMI groups. Urinary incontinence (UI) was more prevalent among overweight and obese women, with a higher risk of UI both at 8 weeks and 12 months after an OASI compared to normal weight women. Overweight and obese women had a lower risk of reporting dyspareunia at 12 months after an OASI compared to normal weight women. Results from the ongoing RCT are pending.

Conclusions: Differences in the AVD during active phase of labor were observed between women with normal weight and those who were overweight or obese. The higher AVD in obese women compared to normal weight women may indicate a valuable anatomical distinction that could be protective for pelvic floor muscles vulnerable during labor. Furthermore, women sustaining an OASI after their first vaginal birth reported distinct complications at 8 weeks and 12 months postpartum based on BMI. Various explanations may underlie these differences in reported complications, including the hypothesis that women with overweight and obesity may experience less extensive involvement of other pelvic floor muscles and nerves, leading to a reduced risk of AI and dyspareunia during the initial postpartum year. Overweight and obese women demonstrated a lower risk of AI and wound complications at 8 weeks, as well as a lower risk of dyspareunia 12 months after a first time vaginal delivery complicated by an OASI. However, the risk of UI was higher among overweight and obese women at both 8 weeks and at 12 months after a first-time vaginal delivery complicated by an OASI. The divergence in complications and symptoms among women in different BMI groups during the initial postpartum year following an OASI underscores the importance of tailored postpartum care, necessitating to individualize advice and follow-ups.