US researchers confirm what many women have long suspected -- pregnancy permanently changes the size and shape of their feet. The study, published in the American Journal of Physical Medicine & Rehabilitation, reported not only did women's feet increase in size during pregnancy, the arch of the foot flattened out and this loss of arch height was permanent. "I had heard women reporting changes in their shoe size with pregnancy, but found nothing about that in medical journals or textbooks," Neil Segal, an associate professor of orthopaedics and rehabilitation at the University of Iowa, said in a statement. "In order to study this more scientifically, we measured women's feet at the beginning of their pregnancy and five months after delivery. We found that pregnancy does indeed lead to permanent changes in the feet." The study tracked 49 pregnant women and collected static and dynamic arch measurements. The researchers found that for about 60 percent to 70 percent of the women in the study, their feet became longer -- up to almost a half-inch -- and wider, as well as a drop in the arch. The study also suggested that first pregnancies may account for most of the observed changes, while second, third, or higher pregnancies may not further alter foot structure.