It is common for expectant mothers to notice their shoes no longer fit as their pregnancy progresses, a phenomenon that often comes as a surprise. This increase in foot size is not merely a single event but the result of several biological and physical changes working together throughout the months of pregnancy. Understanding these underlying mechanisms offers clarity as to why the feet seem to expand both in length and width. This change is a direct consequence of the body adapting to create the best environment for a growing fetus and preparing for childbirth.
The Role of Relaxin
The primary biological driver behind structural changes in the feet is the hormone relaxin. Relaxin is produced early in pregnancy by the ovaries and the placenta, and its levels remain high throughout the gestation period. The hormone’s main function is to loosen and soften the ligaments and joints in the pelvis to accommodate the growing uterus and facilitate delivery. However, relaxin is not confined to the pelvic region; it affects all the ligaments and joints throughout the entire body, including the feet.
The feet contain numerous ligaments and tendons that maintain the arch and hold the small bones in their proper alignment. When relaxin acts on these ligaments, they become more flexible and lax. This hormonal softening allows the bones in the feet to spread slightly, causing the arch to flatten and the foot to lengthen and widen. This structural change is known as arch collapse.
Increased Pressure and Fluid Retention
Beyond hormonal action, physical factors related to pregnancy also contribute significantly to the perceived growth of the feet. A notable increase in overall body mass places considerably more pressure on the arches. The combination of this extra load and the arch-supporting ligaments already loosened by relaxin causes the arch to flatten further. This biomechanical stress, especially noticeable in the later stages of pregnancy, directly results in the foot spreading and requiring a wider shoe size.
Another major contributor to temporary size increase is fluid retention, known as edema. During pregnancy, the body retains more water and experiences an increase in blood volume to support the mother and the developing baby.
The growing uterus also puts pressure on the large veins that return blood from the lower extremities to the heart, slowing circulation. This slowed return of blood contributes to the pooling of fluid in the tissues, leading to noticeable swelling, which is often worse at the end of the day or in hot weather. This swelling is distinct from the structural changes caused by relaxin, as it is a temporary condition that makes the feet feel and appear larger.
Are the Changes Permanent?
Whether the feet will return to their pre-pregnancy size depends on which factor caused the size increase. The temporary swelling from edema typically subsides quickly after delivery, usually within a few weeks, as the body sheds the excess fluid. However, the structural changes caused by the hormonal softening of ligaments may be lasting for some individuals.
If the arch flattening led to a permanent lengthening or widening of the foot structure, the size change can persist. Studies have shown that some women experience an increase in foot length, sometimes up to a full shoe size, which remains after childbirth. Research suggests that any permanent lengthening is most pronounced after the first pregnancy. The structural alteration is a result of the plantar ligaments supporting the arch becoming stretched and elongated.
Comfort Strategies and Prevention
While some structural changes are unavoidable, several strategies can help manage the discomfort and swelling associated with growing feet. To combat edema, it is helpful to elevate the feet above the level of the waist for periods throughout the day to encourage fluid return. Gentle, regular exercise, such as short walks or foot exercises like ankle rotations, can also help improve circulation and reduce fluid pooling.
Wearing the correct footwear is also important, as shoes that are too tight can exacerbate discomfort and restrict circulation. Opting for supportive shoes with a wide toe box and good arch support is recommended to accommodate the changing foot shape and provide necessary support for the flattened arch. Compression stockings or supportive tights can also be beneficial in minimizing swelling by applying gentle pressure to the legs and feet.