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

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.

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.

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).

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