Change in levator ani muscle stiffness and active force during pregnancy and post-partum

It is assumed changes occur to the biomechanics and viscoelastic response of the levator ani muscle during pregnancy; however, there is limited evidence of this. This study used instrumentation and clinical measures to determine the stiffness and active force capacity of levator ani muscle during pregnancy and post-partum, investigated any associations with delivery outcomes, and explored the biomechanical properties associated with symptoms of pelvic floor dysfunction.

This was a prospective observational study, with nulliparous women with a singleton low-risk pregnancy. Data were collected at two stages during pregnancy and post-partum. Measurements included the Australian Pelvic Floor Questionnaire, palpation of active force, and elastometry measurements. Post-partum, 3D/4D ultrasound measurements were included. Repeated measures ANOVAs, pairwise comparisons, Pearson correlation coefficients, and Student's t-tests were used as appropriate.

Fifty-nine women took part in the study. Active force was significantly different over the pregnancy and post-partum, measured with instrumentation (p = 0.002) and palpation (p = 0.006 right, p = 0.029 left). There was no significant change in muscle stiffness during pregnancy. Post-partum muscle stiffness was significantly different between women who gave birth vaginally vs. caesarean section (p = 0.002). Post-partum there were differences in levator hiatal area, symptoms of bladder dysfunction, prolapse symptoms, and sexual dysfunction symptoms.

Active force of the levator ani muscle was significantly reduced during pregnancy and in the post-partum period, while muscle stiffness reduced only in those who had vaginal deliveries.