Parity negatively impacts vaginal mechanical properties and collagen structure in rhesus macaques.

OBJECTIVE: The purpose of this study was to determine the impact of parity on mechanical behavior of the vagina and to correlate these findings with alterations in collagen structure.

STUDY DESIGN: Mechanical properties of 5 nulliparous and 6 parous rhesus macaques were derived from uniaxial tensile tests. Collagen ratios and alignment were quantified by quantitative fluorescent microscopy and picrosirius red staining. Outcomes were compared by the Student t test or Mann Whitney U test (P < .05) and Spearman's rho for correlation coefficients.

RESULTS: Mechanical properties were inferior in a parous vs nulliparous vagina with decreased tangent modulus (P = .03), tensile strength (P < .001), and strain energy density (P = .006). Although no difference in collagen ratios (P = .26) were observed, collagen alignment decreased with parity (P = .06). Worsening pelvic organ support negatively correlated with decreasing collagen alignment (r(2) = -0.66) and mechanical properties (r(2) = -0.67).

CONCLUSION: Vaginal parity is associated with inferior tissue mechanics and loss of collagen alignment. Such behavior likely predisposes to the development of pelvic organ prolapse.