Modelling childbirth: comparing athlete and non-athlete pelvic floor mechanics

There is preliminary evidence that athletes involved in high-intensity sports for sustained periods have a higher probability of experiencing a prolonged second stage of labour compared to non-athletes. The mechanisms responsible for these differences are not clear, although it is postulated that muscle hypertrophy and increased muscle tone in athletes may contribute to difficulties in vaginal delivery. In order to test these hypotheses, we have constructed individual-specific finite element models of the female pelvic floor (one athlete and one non-athlete) and the fetal head to simulate vaginal delivery and enable quantitative analysis of the differences. The motion of the fetal head descending through the pelvic floor was modelled using finite deformation elasticity with contact mechanics. The force required to push the head was compared between the models and a 45% increase in peak force was observed in the athlete model compared to the non-athlete. In both cases, the overall maximum stretch was induced at the muscle insertions to the pubis. This is the beginning of a quantitative modelling framework that is intended to help clinicians assess the risk of natural versus caesarean birth by taking into account the possible mechanical response of pelvic floor muscles based on their size and activation patterns prior to labour.