Approved research

The dilemma of human childbirth and the pelvic floor: A biomechanical approach

Lay summary

Unlike in most animals, the birth process in humans is unusually long and painful. Especially if medical care is not available, it can lead to serious injuries and even to the death of both the mother and the baby. The difficulty mainly arises from a very tight fit between the baby's head and shoulders and the mother's pelvis. It remains puzzling why the pelvic birth canal has not evolved to be wider in order to ease childbirth. Given the high rates of Caesarean section, this puzzle has immediate consequences for public health also in industrialized countries. It is assumed that the tight fit of the birth canal results from the involvement of the pelvis in two conflicting functions, childbirth and upright walking, giving rise to the so-called 'obstetrical dilemma'. In the present project, we will test an alternative hypothesis: the female pelvic canal has evolved by trading off obstetric demands against support of the pelvic floor. In upright humans, the pelvic floor has to resist the pressure exerted from above by the inner organs and the developing fetus. Pelvic floor disorders thus are frequent in humans, and the medical literature suggests that they are related to pelvic dimensions. For the first time, we will test this hypothesis by a novel combination of methods from medical imaging, biostatistics, and engineering. Based on three-dimensional medical images, we will derive a detailed geometric model of the pelvic floor system, including muscles, tendons and ligaments. With pressure values ranging from normal values at rest to high short-lasting pressure during coughing or jumping, we will create a range of cutting-edge biomechanical models to predict the function and possible impairment of the pelvic floor. These biomechanical models will then be applied to the full adult range of pelvic form as well as extrapolations thereof. This will allow us to infer selective regimes on pelvic form and to test if and how obstetric demands of the female pelvic canal have been traded off against pelvic floor support. This interdisciplinary project will last for 24 months and will set new methodological standards in evolutionary and functional anatomy. It is likely to break new grounds in evolutionary medicine and will offer novel perspectives in gynaecology and obstetrics.