Meeting paper
AUGS paper
Biomechanical properties of the vaginal wall: effect of pregnancy, elastic fiber deficiency, and pelvic organ prolapse

Presented at the 28th Annual Scientific Meeting of the American Urogynecologic Society, Hollywood, FL, Sept. 27-29, 2007.
https://doi.org/10.1016/j.ajog.2008.02.022Get rights and content

Objective

The purpose of this study was to identify pregnancy-induced changes in biomechanical properties of the vaginal wall and to compare these with fibulin-5 knockout mice (Fbln5−/−) with and without prolapse.

Study Design

Mid-vaginal segments of nonpregnant and late-pregnant wild-type mice, Fbln5−/− with prolapse mice and Fbln5−/− mice without prolapse were studied. Tissue length at failure, maximal strain, maximal stress, and tissue stiffness were determined.

Results

Compared with nonpregnant mice, vaginas of pregnant and Fbln5−/− (with prolapse) mice exhibited decreased maximal stress, increased distensibility and strain, and decreased stiffness. Tissues from Fbln5−/− mice without prolapse were similar to nonpregnant wild-type animals.

Conclusion

Pregnancy confers remarkable changes in the vaginal wall that include increased distensibility and decreased stiffness and maximal stress. Elastinopathy alone is insufficient to cause significant changes in these properties, but prolapse confers additional alterations in distensibility and stiffness that are similar to those changes that have been observed in pregnancy. These changes may contribute to the poor durability of many restorative surgical procedures for prolapse.

Section snippets

Mice

A total of 25 female mice were studied and killed in accordance with the standards of humane animal care described by the National Institutes of Health Guide for the Care and Use of Laboratory Animals, using protocols that have been approved by the Institutional Animal Care and Use Committee of University of Texas Southwestern Medical Center. Animals were housed under a 12-hour light cycle at 22°C. All wild-type (WT) mice used in these studies were C3BL/6J. Fbln5−/− mice were of a similar mixed

Results

The stress-strain curves of vaginal tissues from late-pregnant animals and nonpregnant controls are shown in Figure 1. In vaginal tissues from nonpregnant WT mice, small increases in strain resulted in marked increases in stress generation that indicated a stiff, nondistensible tissue. In contrast, in vaginal tissues from pregnant animals, large increases in strain resulted in relatively small increases in stress, and stress continued to increase until tissue diameters reached twice that of

Changes with pregnancy

In this study with full-thickness sections of isolated mouse vagina, we found that pregnancy confers remarkable physiologic changes in biomechanical properties. During pregnancy, the resting diameter of the vaginal wall is increased and may distend up to 3 times in diameter, compared with vaginal tissues from nonpregnant animals (ie, 2-fold increase in strain). Tissue stiffness is decreased (ie, distensibility is increased). These appear to be intuitive compensations to allow for parturition.

Acknowledgment

We thank Mr Jesús Acevedo for expert technical assistance.

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This study was supported by National Institutes of Health grant AG028048.

Cite this article as: Rahn DD, Ruff MD, Brown SA, Tibbals HF, Word RA. Biomechanical properties of the vaginal wall: effect of pregnancy, elastic fiber deficiency, and pelvic organ prolapse. Am J Obstet Gynecol 2008;198:590.e1-590.e6.

Reprints not available from the authors.

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