Myogenic changes of the levator ani muscle in premenopausal women: the impact of vaginal delivery and age.

The aim of this study was to evaluate the impact of parity and age on histomorphology of the pelvic floor muscles in female cadavers of reproductive age and to find out whether there is evidence of myogenic or neurogenic muscle injury. In a cross-sectional study 45 premenopausal unfixed and fresh female cadavers were studied. Four groups were defined: nulliparous and parous women under the age of 40 and over 40 years of age. The pelvic floor was biopsied at six standardized locations. For evaluation of the quantitative parameters and fiber type identification, actomyosin ATPase at pH 9.4 was used. For histomorphological evaluation, sections were stained with hematoxylin/eosin, van Gieson, and Gomori trichrome. The circumference of type I fibers is significantly larger in nulliparous women younger than 40 years compared to nulliparae older than 40 years. Comparing these groups, the form factor of type II fibers also increases significantly, presenting a more circular cell form. Compared to nulliparae, vaginal delivery led to a significant difference regarding the presence of centrally located nuclei, fibrosis, and variation in fiber diameter. In nulliparous women, these significant changes were also found with increasing age. In women with a history of vaginal delivery, no further increase in these characteristics could be detected with increasing age. Comparing the three different biopsy sites, all three changes were more pronounced in the ventral part. There was no evidence of grouped fiber atrophy, small angulated fibers, or type grouping in any of the biopsy specimens. Aging and vaginal childbirth lead to histomorphological changes of the pelvic floor muscle that are consistent with changes of myogenic origin. Evidence of neurogenic damage could not be demonstrated.