This has not yet been accurately and precisely documented by research. It is clear however that the changes that occur during pregnancy certainly result in many changes in a woman's body, both temporary and longer lasting. Ligamentous laxity certainly increases during pregnancy as the time to parturition comes closer. Feet and ankles swell, more weight is carried in an unusual location and a variety of mechanical structures may be affected. The back is one of those frequently affected parts.
Back pain is a commonly occurring problem during pregnancy.
A woman with pre-existing scoliosis, will usually have an increase in the curvature occur with each pregnancy. Getting closer to home, for me, the shape of a particular woman's foot may not meet the manufacturers concept of the average woman. This may necessitate a switch to a man's shoe for the individual with a wide forefoot. If this results in the heel being too wide, a thicker sock or one with more heel padding might prevent some of the heel instability that can occur. Shoes can also aggravate pre-existing foot problems and create additional problems for those with the tendency for certain problems to occur.