Many have suspected this for some time, but now science has confirmed it: pregnancy permanently changes the shape and size of a woman's feet.
According to a new University of Iowa study published in the American Journal of Physical Medicine & Rehabilitation, the often-reported loss of arch height associated with pregnancy is not only real, it's permanent.
Researchers believe the foot likely flattens because of two inevitable pregnancy-related symptoms: extra weight and the increased looseness of the joints.
"I had heard women reporting changes in their shoe size with pregnancy, but found nothing about that in medical journals or textbooks," says Neil Segal, M.D., UI associate professor of orthopaedics and rehabilitation. "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."
Bret Ribotsky, president of the American College of Foot and Ankle Orthopedics and Medicine, tells Parenting.com that it's not uncommon for a woman's foot to grow a half size during pregnancy.
"The same hormones that are released to relax the pelvic area also loosen the ligaments in the foot," says Ribotsky. "In addition, the increased body weight of pregnancy lowers the arches, further adding to the foot's length and width."
The University of Iowa study followed 49 pregnant women. Researchers collected both static and dynamic arch measurements of each woman during the first trimester of pregnancy and then again about five months after giving birth.
Researchers discovered that for about 60 to 70 per cent of the women involved in the study, their feet became both longer and wider, with a 2 to 10 mm increase in length.
Most notably, they found that arch height and arch rigidity decreased significantly between the first trimester and five months after childbirth.
While foot changes were undeniable, researchers also noted that first-time mothers are most likely to experience foot changes. Subsequent pregnancies aren't likely to alter foot structure.
Participating in the study were 29 first-time moms, 17 second-time moms, and 3 third-time moms, Discovery News reports.
"We know that women, and especially women who have had children, are disproportionately affected by musculoskeletal disorders," says Segal. "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 hopes to further study how to protect women's musculoskeletal health during pregnancy, and to determine if pregnancy and its related foot changes do, in fact, contribute to arthritis and other problems later on in life.
In the meantime, it's important for pregnant women to accommodate their expanding feet.
"Too-tight shoes weaken the muscles in the ball of the foot and the ligaments that hold the toes straight," says Ronald Smith, M.D., associate professor of orthopedic surgery at Harbor-UCLA Medical Center. "And that can set the stage for foot problems."
Ladies, did your feet change shape and size during pregnancy? Tell us in the comments.