Correlation between maternal body mass index and anovaginal distance in term primiparous women at the time of active labor

Abstract

Introduction: The incidence of obstetric anal sphincter injuries (OASIs) is less in overweight and obese women compared to normal weight women. Aim and objective: The aim of the study was to find a correlation in the thickness of anovaginal distance (AVD) as obtained by transperineal ultrasound between term obese and normal weight primiparous women at the time of active labor. Materials and methods: The study was conducted in the department of obstetrics and gynecology in a tertiary care center in South India. This was a cohort study where term primiparous women at the time of active phase of labor were taken as study population after fulfilling the inclusion criteria. To measure the AVD, a transvaginal ultrasound probe was used in the perineum similar to transperineal ultrasound. The data regarding maternal characteristics, pregnancy details, and the findings at the time of labor were collected from woman’s case sheets from the labor ward. The study population after considering the inclusion criteria were divided into three body mass index (BMI) groups considering the prepregnancy or early pregnancy maternal weight: normal weight (BMI <25), overweight (BMI 25–29.9), and obesity (BMI ≥30). All the three groups were compared according to the measured AVD at the time of labor. Results: There were no significant differences in baseline parameters between the groups. The different BMI groups had mean AVD of 24.2 mm in normal weight group, 24.7 mm in overweight group, and 27.3 mm in the obesity group. There was significant difference (p = 0.028) in AVD between the groups and obese women had significantly thicker AVD as compared to their normal and overweight counterparts. Conclusions: The AVD in obese primiparous group was significantly thick which could be a factor for lower rates of OASI in the obese group. The anal sphincter complex might have been protected by this thicker AVD during the second stage of labor. We recommend further large randomized control trials to evaluate whether there is a correlation between the thickness of the AVD and the incidence of OASI.