Pregnancy might change the size of a woman’s foot permanently. A University of Iowa study examined 49 pregnant women and found that about 60% of them had their feet become wider and longer. It is thought that this might be the result of the hormone relaxin, which helps the pelvis become more flexible in preparation for birth. Relaxin might also affect other ligaments and joints, such as those in the foot. This flexibility, combined with the additional weight of pregnancy, might cause the arch of the foot to become flattened.
More about how pregnancy affects the foot: