Quick Answer
Your feet can actually get permanently bigger when you're pregnant. The extra weight and hormones that relax your ligaments can cause your arches to flatten and your feet to lengthen by up to 10 millimetres. This means you might need a new shoe size even after the baby arrives!
In a hurry? TL;DR
- 1Pregnancy can permanently increase foot length by 2-10mm, equivalent to one or more shoe sizes.
- 2Hormone relaxin softens foot ligaments, while increased weight causes arch flattening and foot lengthening.
- 3These foot structural changes are most common during a woman's first pregnancy.
- 4The foot lengthening and arch flattening are permanent, observable even six months postpartum.
- 5Reduced arch height can lead to altered gait, increased risk of injuries like plantar fasciitis, and potential joint pain.
- 6Permanent foot changes may contribute to women's higher risk of musculoskeletal pain and arthritis in feet, knees, and hips.
Why It Matters
It's surprising that pregnancy can permanently stretch women's feet, meaning their shoe size might change for good.
Many women find that their shoes no longer fit after childbirth, and it is not just due to temporary swelling. Pregnancy can permanently increase foot length by 2 to 10 millimetres, effectively growing a woman's shoe size for life.
Key Changes by the Numbers
- Length increase: 2 to 10 millimetres (up to 0.4 inches)
- Arch height: Significant permanent reduction (flattening)
- Occurrence: Most common during first pregnancies
- Permanent change: Observed six months postpartum and beyond
The Science of the Structural Shift
The permanent change in foot size was documented in a landmark study led by Neil Segal at the University of Iowa, published in the American Journal of Physical Medicine and Rehabilitation. Researchers tracked the foot dimensions of 49 pregnant women from their first trimester to six months after delivery.
The data revealed that for 60 to 70 percent of these women, their feet became longer and wider. Unlike the fluid retention (oedema) that causes temporary puffiness during gestation, this change involved the actual structural integrity of the foot.
Why the Arch Collapses
The shift occurs through a combination of mechanical load and hormonal changes. During pregnancy, the body produces a hormone called relaxin. Its primary job is to loosen the ligaments in the pelvis to facilitate childbirth, but it is not site-specific. Relaxin circulates through the entire body, softening the ligaments that support the 26 bones in the human foot.
Simultaneously, the rapid increase in body mass puts unprecedented pressure on these softened ligaments. The result is a structural flattening of the longitudinal arch. As the arch drops, the foot spreads and lengthens to compensate for the new distribution of weight.
Unlike other physiological changes in pregnancy that revert to a pre-gestational state, these skeletal and ligamentous shifts are often permanent. Once the ligaments have stretched and the arch has descended, the foot remains in its new, elongated shape.
Broader Health Implications
While a bigger shoe size might seem like a minor wardrobe inconvenience, the flattening of the arch (pes planus) can lead to long-term musculoskeletal issues. Reduced arch height changes how weight is distributed across the joints.
- Gait changes: Flattened feet can alter how a person walks, potentially stressing the knees and hips.
- Overuse injuries: There is a higher risk of developing plantar fasciitis or stress fractures due to the lack of shock absorption.
- Arthritis risk: Some researchers suggest that these permanent foot changes may explain why women are at a higher risk for musculoskeletal pain and arthritis in the feet, knees, and hips compared to men.
Related Small Talk Knowledge
- The history of shoe sizing: How standardisation began
- Why human hips are narrower than our ancestors
- The biology of ligament repair
Does this happen with every pregnancy?
Research suggests the most significant changes occur during the first pregnancy. Subsequent pregnancies do not typically cause the foot to lengthen further, as the initial stretching of the ligaments has already occurred.
Can exercise prevent the feet from growing?
While strengthening the intrinsic muscles of the foot can help support the arch, it cannot entirely counteract the effects of relaxin and significant weight gain on the ligaments. Supportive footwear during pregnancy may mitigate some flattening.
Is the change always both feet?
Yes, the hormonal and weight-bearing effects are systemic, meaning both feet are generally affected equally, though minor natural asymmetries may exist.
Key Takeaways
- Permanent Growth: Pregnancy can add up to 0.4 inches to foot length.
- Structural Shift: The change is caused by arch flattening, not bone growth.
- Hormonal Impact: Relaxin loosens ligaments, allowing the foot to spread under weight.
- First-Time Effect: Most structural changes happen during the first child.
- Health Risk: Permanent foot changes may contribute to knee and hip pain later in life.
If you are planning a family, you might want to wait before investing in that designer shoe collection. Your current size might literally be a thing of the past.
