Many women notice that their shoes fit differently during and after pregnancy. Scientific studies confirm that pregnancy can alter the size and shape of the feet. The change often involves an increase in both foot length and width, resulting from the body’s adaptation to carrying a baby.
The Biological Mechanisms of Foot Expansion
The primary mechanism driving foot changes is the systemic effect of the hormone relaxin, which the body produces in large quantities during pregnancy. Relaxin’s main role is to loosen the ligaments and joints in the pelvis to prepare for childbirth, but its effect is not localized to the pelvic region. The hormone acts throughout the body, causing an increased laxity in all connective tissues, including the ligaments that support the arches of the feet. This softening of the ligaments makes the foot structure more pliable and susceptible to stretching under pressure.
This hormonal effect is compounded by the significant increase in body weight, especially in the later trimesters. The greater load on the feet, combined with increased ligament flexibility, causes the arches to flatten and lengthen. The forward shift in the center of gravity and change in gait also adds stress to the foot structure.
A third factor is edema, or fluid retention, common during the third trimester. As the growing uterus puts pressure on the veins in the lower body, and as blood volume increases by up to 50%, fluid can accumulate in the lower extremities due to gravity. This temporary swelling in the feet and ankles causes a noticeable increase in volume, making shoes feel tight and uncomfortable.
Manifestation of Foot Changes
The physical manifestation of these biological changes involves two distinct types of alteration: temporary swelling and permanent structural change. The most common structural change is a decrease in arch height, resulting in acquired flatfoot, or pes planus. When the ligaments that form the longitudinal arch of the foot stretch and weaken, the arch collapses downward, and the foot elongates.
This arch collapse increases foot length, typically between 2 and 10 millimeters, and also causes widening. For many women, this translates to an increase of about a half-size to a full-size in shoe length. The change in foot size is typically more pronounced during a woman’s first pregnancy.
The temporary swelling caused by edema contributes to tightness and makes the foot appear wider and puffier, particularly at the end of the day. This swelling usually resolves relatively quickly after delivery as the body eliminates the excess fluid.
Duration and Long-Term Implications
The temporary swelling from fluid retention dissipates within a few weeks postpartum as hormonal levels normalize and excess fluid is shed. However, the structural changes resulting from ligament laxity and prolonged weight-bearing are often permanent.
Research suggests that for a significant percentage of women, the loss of arch height and resulting increase in foot length persist long after the baby is born. This means a woman who experienced a permanent arch drop will likely need to purchase new shoes in a larger size to accommodate the newly elongated foot.
If the structural change leads to persistent overpronation or pain, consulting a podiatrist may be beneficial. They can assess the new foot position and recommend supportive footwear or custom orthotics to stabilize the foot. This can prevent secondary pain in the knees, hips, or back, helping women manage their foot health and shoe selection going forward.