Pregnancy- and delivery-induced biomechanical changes in rat vagina persist postpartum

We sought to define changes in vaginal distensibility (VD) induced by pregnancy and vaginal delivery using a novel in vivo biomechanical testing protocol. Under sedation, a balloon was inserted into the vagina of 27 virgin, pregnant and 4-week postpartum Long-Evans rats and incrementally distended. Pressure-volume curves were generated with slopes characterizing VD (higher slope = less distensible). One-way ANOVA with a Bonferroni post-hoc test were used for statistical analyses. Mean pressures at an infusion volume of 1 cc were lower in pregnant and postpartum rats than in virgins (P < 0.001). VD was increased in pregnant vs. virgin rats (P < 0.001) and did not recover to virgin levels post partum (P < 0.001). We have developed a test that measures VD in vivo under clinically relevant loading conditions. The increased VD in the late postpartum period defines a persistent change in biomechanical behavior of the vagina related to pregnancy and vaginal delivery.