Swollen feet during pregnancy: why?

Pregnancy is accompanied by a range of hormonal, physiological, and physical changes. Among these, one can find the swelling of the feet and lower limbs in general. Approximately 8 out of 10 women notice an increase in the diameter of their feet during pregnancy, often by about fifty millimeters. It is sometimes considered that this change is a consequence of the weight gain experienced by pregnant women. However, while it has indeed been demonstrated that mechanical stress induces a remodeling of the skin tissues, scientists believe it is unlikely that the weight gain associated with pregnancy persists long enough to induce such changes. Therefore, the cause of swollen feet during pregnancy lies elsewhere.

Excessive swelling of the feet during pregnancy, sometimes referred to as edema, is actually due to the accumulation of fluid or fat in the ligaments, caused by hormonal changes. Indeed, a generalized softening of the connective tissue is observed in pregnant women. A large part of this connective tissue is located in the skin, so it is natural to observe some swelling. Indeed, during pregnancy, the adrenal glands produce a large amount of aldosterone and cortisol. The former is a steroid hormone whose main role is to regulate the sodium-potassium balance and the osmotic pressure in the body, which has a direct influence on water retention. Cholesterol, on the other hand, is a lipid of cell membranes serving as a precursor for the synthesis of steroid hormones, including aldosterone.

Furthermore, swelling of the lower limbs during pregnancy is facilitated by the growth of the uterus. Indeed, as it expands to accommodate the developing fetus, it exerts increasing pressure on the blood vessels located in the pelvic region, particularly on the inferior vena cava and pelvic veins. This compression slows venous return, that is, the upward flow of blood from the lower limbs towards the heart, thus creating a buildup of blood in the veins of the legs and feet. This partial obstruction of blood flow increases venous pressure, pushing fluids out of the blood vessels into the surrounding tissues, which causes edema.

Beyond the mechanical pressure of the uterus, the increase in blood volume, which can reach up to 50%, creates an additional burden on the circulatory system. This intensification is necessary to meet the increased oxygen and nutrient needs of the fetus, but it can also exacerbate edema. It appears to be primarily due to an increase in estrogen production. By binding to nuclear receptors ER-α and ER-β, this hormone triggers a cascade of reactions leading to an elevation in the amount of intracellular cyclic adenosine monophosphate (cAMP). However, cAMP is involved in the regulation of nitric oxide (NO) synthesis, a vasodilator.

While it's normal to experience slight swelling in the feet during pregnancy, a significant increase in their size should raise concern as it could be due to a more serious issue: in such cases, it is imperative to consult your doctor without delay.

To limit the swelling of the feet during pregnancy, it is particularly recommended to elevate your legs when possible, engage in gentle physical activity, and wear compression stockings and comfortable shoes. Additionally, a recent study has shown that massaging your feet with warm water can help improve blood circulation. For five days, a daily thirty-minute massage with warm water was performed on 31 pregnant women presenting with foot edema. The severity of the edema, rated from 0 to 4, was evaluated before and after the intervention. The results are compiled in the table below and show an overall decrease in swelling. It would be interesting if these results could be reproduced in other clinical trials to be fully verified.