The impact of different birth weights on the incidence of maternal pelvic floor dysfunction and the value of ultrasound evaluation: A single-center retrospective study

Abstract

This study investigates the impact of different newborn birth weights on the incidence of early postpartum pelvic floor dysfunction (PFD) in mothers and evaluates the value of perineal ultrasound in risk assessment. A total of 168 women who delivered at our hospital between June 2023 and May 2025 and completed a 6- to 8-week postpartum follow-up were included. All participants had full-term, single, head-first, vaginal deliveries. Newborns were categorized into 4 birth weight groups: Q1 (≤3080 g), Q2 (3081–3365 g), Q3 (3366–3680 g), and Q4 (≥3681 g). Demographic, delivery-related data, and postpartum PFD outcomes (stress urinary incontinence, pelvic organ prolapse ≥ II, and puborectal muscle tears) were collected. All women underwent 3D perineal ultrasound at 6 to 8 weeks postpartum to measure perineal area, bladder neck descent, and urethral rotation angle. Univariate and multivariate logistic regression analyses were used to assess risk factors, and ultrasound subgroup interaction analysis was performed. No significant differences were found in age, parity, or newborn gender among the groups. However, the high birth weight group had significantly higher prepregnancy body mass index, gestational age, and labor duration, as well as a higher episiotomy rate (P < .05). Postpartum follow-up showed that PFD incidence increased with newborn birth weight (Q1 19.0% vs Q4 52.4%, P = .003), with stress urinary incontinence and pelvic organ prolapse ≥ II more common in the high birth weight group. Ultrasound results indicated larger perineal area, anteroposterior diameter, transverse diameter, bladder neck descent, posterior bladder-urethra angle, and urethral rotation angle in the high birth weight group (all P < .01). Multivariate analysis confirmed that Q4 newborns (odds ratio = 3.92), prolonged second stage of labor, and certain ultrasound parameters were independent risk factors. Subgroup analysis showed high birth weight had a more significant risk effect in certain ultrasound parameter thresholds (odds ratio 2.77–3.64, all P < .05). Increased newborn birth weight is a significant independent risk factor for early postpartum PFD, likely through prolonged labor and increased pelvic floor injury. Perineal ultrasound is valuable for risk identification and early screening. Further multicenter studies are needed to confirm the causal relationship between birth weight and pelvic floor injury.