A total of 52 women aged 18 to 43 years of age were accepted into the study, with post-partum measures completed on 45 participants. See Table One for demographics and clinical characteristics. Preliminary analysis of the results for this abstract focus on the elastometry measurements.
Average muscle stiffness was measured as 690 N/m ± 180 N/m at 18 to 24 weeks, 638 N/m ± 169 N/m at 35 to 38 weeks, and 668 N/m ± 232 N/m post-partum. However, these differences were not statistically significantly different, F(1.51, 40.74) = 0.93, p = 0.377.
Active force at 50 mm aperture decreased progressively from the initial assessment in the second trimester to the post-partum assessment. Initial measures of active force were 8.2 N ± 4.0 N at 18 to 24 weeks, reducing to 7.3 N ± 3.5 N at 35 to 38 weeks, to final post-partum measurements of 6.4 N ± 3.1 N. The differences were statistically significant, F(1.75, 41.91) = 7.69, p = 0.002. In pairwise comparisons, the difference was significant between 18 to 24 weeks and post-partum, a decrease of 1.8 N (95% CI, 0.46 to 3.1), p = 0.006. This represents a 22 % reduction in active force over the childbearing year (Figure One).
Multivariate regression modelling was completed for each time point to investigate the effect of potential explanatory variables on the response variables (stiffness and active force). At 18 to 24 weeks, an increase in passive force of 1 N predicts a corresponding increase in muscle stiffness of 34.0 N/m, p < 0.001, while an increase in active force of 1 N is predictive of a decrease in muscle stiffness of 7.5 N/m, p = 0.045. At 35 to 38 weeks, an increase in passive force of 1 N predicts a corresponding increase in muscle stiffness of 47.5 N/m, p < 0.001. Post-partum, an increase of the following variables were predictive of an increase in muscle stiffness: passive force of 1 N (increase of 60.7 N/m, p < 0.001); increase of 1 year of age (increase of 10.8 N/m, p = 0.004); and levator hiatal area increase of 1 cm2 (increase of 20.1 N/m, p = 0.013). The following variables were predictive of a decrease in muscle stiffness: BMI increase by 1 kg/m2 (decrease of 10.3 N/m, p = 0.026); and levator hiatal area increased by 1 cm2 on maximum pelvic floor muscle contraction (decrease of 29.3 N/m, p = 0.002).
None of the chosen explanatory variables demonstrated any effect on active force at any of the time points.