Pregnancy commonly changes the size and shape of a woman’s feet, researchers from the University of Iowa reported in the March issue of the American Journal of Physical Medicine & Rehabilitation. The authors added that the change is permanent.

Women commonly develop flat feet during pregnancy, possibly because the extra weight flattens out the arch of the foot. Also, the joints tend to be looser during pregnancy. There is a hormone the body produces during pregnancy called relaxin that facilitates the birth process by causing a lengthening and softening of the cervix and the pubic symphysis (where the pubic bones meet). Relaxin also allows the ligaments in the feet to stretch. The investigators suggest that this loss of arch height is permanent.

Neil Segal, associate professor of orthopaedics and rehabilitation, said:

“I had heard women reporting changes in their shoe size with pregnancy, but found nothing about that in medical journals or textbooks. 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.”

Segal and team followed 49 women, all of them pregnant, during their first trimester of pregnancy and then again approximately five months after they had given birth. They collected dynamic and static arch measurements.

The team found that in the majority of the women (60%-70%), their feet became wider and longer.

The women’s arch height and arch rigidity fell considerably from the first trimester to five months after their child was born. This resulted in the length of their feet increasing by between 2mm and 10mm.

However, they did not detect any significant change in the distribution of foot pressure.

The changes in foot length and width seem to occur only during the first pregnancy, the investigators noted.

Segal said “We know that women, and especially women who have had children, are disproportionately affected by musculoskeletal disorders. It is possible that these foot changes that occur during pregnancy may help explain why, in comparison with men, women are at higher risk for pain or arthritis in their feet, knees, hips, and spines.”

Segal and colleagues want to find out whether these alterations in foot size and shape might lead to health problems later on, such as arthritis. They are currently looking into how a woman’s musculoskeletal health can be better protected during pregnancy.

English actress, Denise van Outen, mentioned two years ago that her feet grew from a size five to six while she was pregnant, and stayed at six. She added that she had to give away most of her shoes after her baby Betsy Mead was born.

The study was sponsored in part by grants from the National Institute on Aging and the American Geritrics Society.

Written by Christian Nordqvist