Assessment of the Impact of Vaginal Delivery on the Levator Ani Muscle Using Intravoxel Incoherent Motion MRI.

INTRODUCTION AND HYPOTHESIS: This study aimed to characterize levator ani muscle (LAM) injury using conventional magnetic resonance imaging (MRI) following the first vaginal delivery and evaluate the feasibility of intravoxel incoherent motion (IVIM) imaging for its assessment.

METHODS

This prospective study included 81 primiparous women post-vaginal delivery (primiparous group) and 54 nulliparous women (nulliparous group). All participants underwent pelvic floor MRI on the day of enrollment; primiparous women were scanned at 6 weeks postpartum (window 0-3 days). The imaging protocol included T2-weighted and IVIM sequences, followed by postprocessing. Morphological changes in LAM were described using a conventional MRI-based scoring system. IVIM parameters-including the pure diffusion coefficient (D), pseudo-diffusion coefficient (D*), and perfusion fraction (f) of left and right puborectalis and iliococcygeal muscles-were measured.

RESULTS

Morphological injuries to the puborectalis and iliococcygeus were identified in 28 (34.57%) and nine (11.11%) primiparous women, respectively, whereas no LAM injuries were detected in the nulliparous group. Primiparous women exhibited higher puborectalis D values and lower puborectalis f values compared with nulliparous women (both P < 0.05), whereas puborectalis D* and all iliococcygeus IVIM parameters showed no significant differences. After adjusting for age, height, weight, and body mass index, partial correlation analyses revealed a weak-to-moderate positive correlation between puborectalis D values and conventional MRI-based LAM injury scores, and a weak negative correlation was observed between puborectalis f values and these scores.

CONCLUSIONS

LAM injury at 6 weeks postpartum was associated with vaginal delivery based on conventional MRI findings. IVIM imaging may reflect pathophysiological changes in water diffusion and microcirculatory perfusion associated with LAM injury after vaginal delivery, although further validation is required.