Relaxing Blamed for Changing Foot Size in Pregnancy

You know what they say about men with big feet? Yes, big shoes. Well now they say the same thing about pregnant women because having a baby fundamentally and very commonly changes the shape of mothers feet. They become bigger and they don’t revert to their original shoe size after the birth either. It is researchers at the University of Iowa in this month’s publication of the American Journal of Physical Medicine and Rehabilitation, who are giving us the big news.

Flat feet are definitely a side effect of being with child. Any new mother would tell you that and they would also tell you why. The prolonged carrying of all those lovely extra pounds pressing on the arches and spreads the bones of the feet. Buy as if this were not enough the joints within the feet are softer and prone to stretching. It is all down to an eponymous hormone, produced during pregnancy, called ‘relaxin’.

No pregnant mom would want to be deficient in relaxin, because its primary function is to ease the actual giving of birth. Relaxin causes the cervix and the pubic symphysis, that’s where the pubic bones meet, to increase in length and to become softer in readiness for passage of the baby. However relaxin has the same effect on the ligaments in between the bones of the feet. Once your arches have started to drop there is no getting them back.

The new study’s author, an orthopaedic and rehabilitation specialist describes the starting point for this research thus:

“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.”


Forty nine expectant mothers had their feet measured every which way in the first twelve weeks of their pregnancy. This data was then compared with the same measurements taken again about twenty weeks after the birth of their children. Thirty four of the subjects were found to have wider and longer feet. Most significantly the height of the arches of the feet were noticeably lower and less rigid after the birth, and it is this that pushed the feet anywhere between 2 and 10 millimeters outwards. Interestingly there was no measurable changes in the spread of downward foot pressure. Luckily for the mothers of big families these physiological changes only occurred during child number one.

“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.”

On-going research will go in two directions. Firstly it will aim to uncover the link between changing feet during pregnancy and on-going health issues such as arthritis. Secondly it will aim to help pregnant women to protect their bones and muscles better.

Claire Al-Aufi

Claire Al-Aufi is a contributing author for Hive Health Media who provides updates on health and fitness news.

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