Fluid Retention in Pregnancy

Swelling and Fluid Retention During Pregnancy: Physiological Mechanism

Fluid retention, manifesting as swelling (edema), is one of the most common pregnancy symptoms, especially in the third trimester. It is a physiological and expected process, related to the body's adaptation to the needs of the growing baby. Understanding why your body retains water will help distinguish normal from pathological.

Why does a pregnant body retain fluid?

The phenomenon is based on a combination of reasons:

• Increased fluid volume in the body: During pregnancy, blood volume and interstitial fluid increase by almost 50% (by 6-8 liters). This extra fluid is needed to support the placenta, amniotic fluid, and the increased blood flow.
• Mechanical pressure of the uterus: The growing uterus presses on the large veins in the pelvis, slowing the return of blood from the legs to the heart. This raises pressure in the vessels of the lower limbs and "pushes" fluid from capillaries into surrounding tissues.
• Hormonal changes: Pregnancy hormones, notably aldosterone, promote sodium retention in the body, and sodium, in turn, "pulls" water with it.

When are swelling considered normal?

Physiological swelling is usually symmetrical, appears on the feet and ankles, worsens by evening (especially after prolonged standing or in heat) and significantly decreases after a night’s rest. However, it is important to be aware of warning signs. Sudden and severe swelling of the face and hands can be a sign of preeclampsia, especially when combined with high blood pressure. Read about general mechanisms on the page "Fluid Retention".