Vaginal wall weakness in parous ewes: a potential preclinical model of pelvic organ prolapse

Ewes develop pelvic organ prolapse (POP) and may be a suitable model for preclinical studies evaluating cell-based therapies for POP. The aim of this study was to establish a clinical score of vaginal weakness and to compare POP Quantification System (POP-Q) values in conscious nulliparous and parous ewes and determine whether ewes are a suitable POP model.

Ewes (n = 114) were examined while conscious, without sedation, and standing in a V conveyer by adapting the human POP-Q measurement. Ovine POP was defined as descent to the introitus from POP-Q points Aa 3 cm above the introitus on the anterior wall, Ap 3 cm above the introitus on the posterior wall, or increased Ba anterior wall descent above the urethra (≥0). A test-retest showed good inter- and intrarater reliability.

There was no evidence of tissue mobility at Aa, Ap, Ba (all -3 cm) in nulliparous ewes (n = 14). In contrast, multiparous ewes had a median of -1 and interquartile range (IQR) (-2 to 0) for Aa, [0 (-1 to 0)] for Ap and [0 (-2.75 to 0)] for Ba (n = 33; P < 0.0001 in comparison with nulliparous) ewes. Ovine vaginal displacement was seen in 50.9 % of parous ewes and was strongly associated with parity (P = 0.003).

A modified POP-Q in conscious ewes was established showing that the vaginal wall of parous animals has similar regions of weakness as do women and may be similarly related to parity. Ewes appear to be a representative preclinical model of human vaginal prolapse.