Biomechanics of the rat vagina during pregnancy and postpartum: a 3-dimensional ultrasound approach

Changes of pelvic organ prolapse and pelvic floor dysfunction throughout pregnancy in singleton primigravidas: A prospective cohort study

OBJECTIVE

To document the deterioration in pelvic organ support occurring throughout all trimesters during the first pregnancy of women with no known risk factors. Secondarily to make a comprehensive review in order to verify the current findings and methodologies of similar studies in the literature.

STUDY DESIGN

In this prospective study, forty-one primigravid women with a singleton pregnancy were recruited during their first trimester. During follow-up pelvic organ support changes were documented by using Pelvic Organ Prolapse Quantification (POP-Q) system. Additionally, pelvic floor muscle strength examination, by modified Oxford scoring (MOS), and symptom assessment by Pelvic Floor Distress Inventory-Short Form (PFDI-20) were performed at three time points: first (T1), second (T2), and third trimester (T3) (n = 33). The Wilcoxon test was performed to test the significance of pairwise differences. Spearman correlation coefficient was estimated to determine the linear association of the findings.

RESULTS

Both distal and proximal anterior and posterior vaginal walls (Points Aa, Ba, Ap and Bp) with cervix (C) descended towards the hymen, throughout first pregnancy with a significant caudal shift on progressing from T2 to T3 (p ≤ 0.017). Posterior fornix (Point D) made a non-significant cranial shift (p = 0.527). The genital hiatus, perineal body and total vaginal length increased significantly (p ≤ 0.001). No significant difference in MOS was observed throughout pregnancy. The scores of PFDI-20 with all its domains worsened significantly during pregnancy, especially in T3 (p ≤ 0.011). Moderate correlations were observed between posterior vaginal descent and anorectal symptoms (rho 0.427, p < 0.05), and between the changes in genital hiatus and prolapse symptoms (rho 0.406, p < 0.05).

CONCLUSION

A significant descent both in all compartments of vaginal wall and perineum with an increase in total vaginal length, was observed together with an associated pelvic floor dysfunction throughout the first pregnancy of women.

Animal models for pelvic organ prolapse: systematic review

INTRODUCTION AND HYPOTHESIS

We aimed to summarize the knowledge on the pathogenesis of pelvic organ prolapse (POP) generated in animal models.

METHODS

We searched MEDLINE, Embase, Cochrane and the Web of Science to establish what animal models are used in the study of suggested risk factors for the development of POP, including pregnancy, labor, delivery, parity, aging and menopause. Lack of methodologic uniformity precluded meta-analysis; hence, results are presented as a narrative review.

RESULTS

A total of 7426 studies were identified, of which 51 were included in the analysis. Pregnancy has a measurable and consistent effect across species. In rats, simulated vaginal delivery induces structural changes in the pelvic floor, without complete recovery of the vaginal muscular layer and its microvasculature, though it does not induce POP. In sheep, first vaginal delivery has a measurable effect on vaginal compliance; measured effects of additional deliveries are inconsistent. Squirrel monkeys can develop POP. Denervation of their levator ani muscle facilitates this process in animals that delivered vaginally. The models used do not develop spontaneous menopause, so it is induced by ovariectomy. Effects of menopause depend on the age at ovariectomy and the interval to measurement. In several species menopause is associated with an increase in collagen content in the longer term. In rodents there were no measurable effects of age apart of elastin changes. We found no usable data for other species.

CONCLUSION

In several species there are measurable effects of pregnancy, delivery and iatrogenic menopause. Squirrel monkeys can develop spontaneous prolapse.

Tissue biomechanical behavior should be considered in the risk assessment of perineal trauma at childbirth

Perineal trauma at childbirth is associated with strong negative impacts on a woman's health but remains unpredictable. Pregnancy induces several changes in biomechanical behavior in humans as in animals, namely, an increase in ligamentous laxity and an increase in vaginal distensibility. Pelvic floor muscles in rats are reported to exhibit specific behaviors during pregnancy. Increases in both stiffness and the number of sarcomeres in series are observed and might process that protect against perineal trauma at childbirth. Some data in humans have shown that the risk of perineal trauma is highly linked to the intrinsic characteristics of the tissue, suggesting the potential benefit of incorporating intrinsic biomechanical characteristics in the risk prediction for perineal trauma. Shear wave elastography might be a useful noninvasive tool to investigate the elastic properties of these tissues in pregnant women in vivo, with the goal of implementing these properties as a predictive strategy.

Multimodal imaging assessment and histologic correlation of the female rat pelvic floor muscles' anatomy

Pelvic floor disorders negatively impact millions of women worldwide. Although there is a strong epidemiological association with childbirth, the mechanisms leading to the dysfunction of the integral constituents of the female pelvic floor, including pelvic floor skeletal muscles, are not well understood. This is in part due to the constraints associated with directly probing these muscles, which are located deep in the pelvis. Thus, experimental models and non-invasive techniques are essential for advancing knowledge of various phenotypes of pelvic floor muscle injury and pathogenesis of muscle dysfunction, as well as developing minimally invasive approaches for the delivery of novel therapeutics. The most widely used animal model for pelvic floor disorders is the rat. However, the radiological anatomy of rat pelvic floor muscles has not been described. To remedy this gap, the current study provides the first detailed description of the female rat pelvic floor muscles' radiological appearance on MR and ultrasound images, validated by correlation with gross anatomy and histology. We also demonstrate that ultrasound guidance can be used to target rat pelvic floor muscles for possible interventional therapies.