Pregnancy may increase a woman's foot size, a change that appears to be permanent, according to a new study.

Researchers measured the arch height and foot length of 49 women during their pregnancy and five months after they had given birth. On average, the women's arch height decreased, and in turn, their foot length increased between 2 and 10 millimeters (about 0.1 to 0.4 inches) — during this period.

Overall, about 60 to 70 percent of the women had longer feet and shorter arches after childbirth, the researchers said. Eleven of the women reported changes in their shoe size, the researchers said.

While previous studies have documented changes in foot size during pregnancy, none had looked to see if the changes persisted after delivery. “I heard so many women talking about having to go buy new shoes after pregnancy,” said study researcher Neil Segal, an associate professor of orthopaedics and rehabilitation at the University of Iowa. This prompted Segal to look into the issue further.

In an earlier study, Segal surveyed about 110 women at a mall, and asked if their shoe size had ever changed during their adult years. While just 13 percent of women who'd never been pregnant said it had, between 30 to 60 percent of women who had been pregnant at least once said their shoe size had changed.

The change in foot size may be due to the extra weight women carry around during pregnancy, which puts greater stress on the feet, and, thus, may flatten the arch, the researchers said. In addition, pregnant women produce hormones that increase the looseness of the joints and ligaments (tissue that connects bone to bone), possibly making the foot structure more malleable.

Most of the women involved in the new study who experienced changes in their foot length and arch height were first-time mothers. Women had given birth to two or three children did not experience such significant changes. This result suggests that a woman's first pregnancy may have the greatest impact on foot size, the researchers said. But a larger study will be needed to confirm this, Segal added. (Twenty-nine of the women in the study were first-time moms; 17 were second-time moms, and three were third-time moms.)

Changes in the feet during pregnancy may explain why women are at increased risk for pain or arthritis in their feet, knees, hips and spine than men, Segal said. A flattened foot can strain the ligaments in the foot's sole, causing changes in gait that put extra strain on the knees, Segal said.

Segal plans to do more studies to determine if foot changes during pregnancy do indeed lead to other health problems, such as arthritis. He also plans to investigate whether modifying the footwear of pregnant women  can prevent foot flattening..

The study will be published in the March issue of the  American Journal of Physical Medicine & Rehabilitation.

Pass it on: Pregnancy may slightly increase the length and width of women's feet, a new study suggests.

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