Ovine multiparity is associated with diminished vaginal muscularis, increased elastic fibres and vaginal wall weakness: implication for pelvic organ prolapse

Abstract

Pelvic Organ Prolapse (POP) is a major clinical burden affecting 25% of women, with vaginal delivery a major contributing factor. We hypothesised that increasing parity weakens the vagina by altering the extracellular matrix proteins and smooth muscle thereby leading to POP vulnerability. We used a modified POP-quantification (POP-Q) system and a novel pressure sensor to measure vaginal wall weakness in nulliparous, primiparous and multiparous ewes. These measurements were correlated with histological, biochemical and biomechanical properties of the ovine vagina. Primiparous and multiparous ewes had greater displacement of vaginal tissue compared to nulliparous at points Aa, Ap and Ba and lower pressure sensor measurements at points equivalent to Ap and Ba. Vaginal wall muscularis of multiparous ewes was thinner than nulliparous and had greater elastic fibre content. Collagen content was lower in primiparous than nulliparous ewes, but collagen organisation did not differ. Biomechanically, multiparous vaginal tissue was weaker and less stiff than nulliparous. Parity had a significant impact on the structure and function of the ovine vaginal wall, as the multiparous vaginal wall was weaker and had a thinner muscularis than nulliparous ewes. This correlated with “POP-Q” and pressure sensor measurements showing greater tissue laxity in multiparous compared to nulliparous ewes.

Morphological and Functional Changes in the Vagina following Critical Lifespan Events in the Ewe

“…Also the findings on elastin content parallel what was earlier described in ewes. Our primiparous ewes displayed an increased elastin density which is in agreement with observations of Emmerson et al [34]. In multiparous ewes, the density increased in the middle vagina, a trend also observed in 2 other studies [34,40].…”

“…The laxity of the distal vagina increased after first vaginal delivery, which is in line with our previous study and with the study performed by Emmerson et al [17,34]. In the sheep of this study, the distal vagina became stiffer after multiple deliveries.…”

“…Our primiparous ewes displayed an increased elastin density which is in agreement with observations of Emmerson et al [34]. In multiparous ewes, the density increased in the middle vagina, a trend also observed in 2 other studies [34,40]. Clinical observations we cannot really give, as the few studies on elastin in clinical vaginal specimens we are aware of, are in women with POP and urinary incontinence [35].…”

“…In our ewes, following a single vaginal delivery, the distal vaginal wall contained less collagen, as previously measured by hydroxyproline assay and reported by Emmerson et al [34]. Thereafter, in multiparous and even more so after castration, the collagen density increased, the first already described in literature [34]. Our semi-quantitative findings in collagen parallel the changes in stiffness.…”

“…In the sheep of this study, the distal vagina became stiffer after multiple deliveries. This finding is not in concordance with that of Emmerson et al [34] yet in that study the animals were half the age (3-4 years) of that of our (4.5-9.5 years) sheep. To our knowledge, no robust clinical data on this matter are available.…”