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

Abstract

The vagina and surrounding structures have been shown to remodel during pregnancy. Our objective was to characterize the biomechanical properties of the vagina in the rodent model in vivo utilizing three-dimensional (3D) ultrasound. The vagina was visualized by ultrasound after distention by increasing pressures throughout pregnancy (15 and 18days) and after vaginal delivery (7 and 30days postpartum) of six longitudinally followed rodents. The pelvic floor compliance and vaginal cross-sectional area of the proximal, middle, and distal vagina were compared with those of nulliparous control animals (n = 8). The compliance of the pelvic floor increased 3.5- and 5.4-fold at days 15 and 18 of pregnancy respectively (p < 0.05). The compliance of the pelvic floor decreased 7days postpartum, and it continued to decrease after vaginal delivery through the 30day time point. Using 3D ultrasound, we could characterize the remodeling of the vagina throughout pregnancy and after vaginal delivery. We could reconstruct the vaginal wall cross-sectional area and found the distal vaginal wall throughout pregnancy to be distended more than the proximal and middle regions. The observed changes in vaginal area may improve our understanding of which areas are at risk of injury during delivery. Further, 3D ultrasound allowed the determination of the in vivo biomechanical properties of the vagina. This image modality is beneficial for characterizing the in vivo properties of the vagina and surrounding pelvic support longitudinally within an animal.