What causes foot swelling during pregnancy?

Causes of Foot Swelling During Pregnancy

Foot swelling during pregnancy is primarily caused by compression of the iliac veins by the enlarging uterus, combined with pregnancy-induced physiological changes including increased blood volume and hormonal alterations that lead to venous stasis. 1

Physiological Mechanisms

Foot swelling (edema) during pregnancy results from several interconnected factors:

1. Mechanical Compression:

   • The enlarging uterus compresses the iliac veins, particularly the left iliac vein (explaining why 85% of pregnancy-related DVT cases occur on the left side) 1
   • This compression impairs venous return from the lower extremities

2. Cardiovascular Changes:

   • Blood volume increases by 40% by 24 weeks gestation 1
   • Cardiac output increases 30-50% during normal pregnancy 1
   • Systemic vascular resistance decreases due to active vasodilation 1

3. Hormonal Factors:

   • Increased relaxin hormone, especially in the third trimester, leads to ligament laxity 2
   • This causes feet to become longer, flatter, and broader (sometimes permanently) 2, 3
   • Prostacyclin and nitric oxide mediate vasodilation 1

4. Hematological Changes:

   • Pregnancy induces hypercoagulability with increased coagulation factors, fibrinogen, and platelet adhesiveness 1
   • Diminished fibrinolysis further contributes to venous stasis 1

Timing and Progression

• Swelling typically worsens as pregnancy progresses, becoming most pronounced in the third trimester 2
• Diastolic blood pressure gradually increases in the third trimester, potentially affecting fluid distribution 1
• Foot health status declines throughout pregnancy, particularly in areas of footwear comfort, physical activity, and vigor 2

Clinical Presentation

Leg swelling is a frequent finding in pregnancy and may present as:

• Bilateral foot and ankle edema (most common)
• Left-sided swelling (more common due to anatomical factors) 1
• Calf circumference difference of ≥2cm (may indicate DVT) 1

Risk Factors for Excessive Edema

• Lack of physical exercise during pregnancy 4
• Pre-existing venous conditions (vascular insufficiency, history of thrombosis) 4
• Prolonged standing or sitting
• Increased BMI
• Dehydration

Distinguishing Normal from Pathological Swelling

It's crucial to differentiate normal physiological edema from pathological conditions:

• Normal edema: Bilateral, worse at the end of the day, improves with elevation
• Concerning signs (requiring medical evaluation):
  • Sudden onset of swelling
  • Unilateral leg swelling (especially left leg)
  • Associated with pain, redness, or warmth
  • Accompanied by shortness of breath or chest pain

Management Approaches

For normal physiological edema:

1. Physical measures:

   • Graduated compression stockings (recommended for high-risk women) 1
   • Regular physical activity (helps prevent edema) 4
   • Elevation of legs when resting
   • Avoiding prolonged standing or sitting

2. Water immersion:

   • Standing in water for 20 minutes has been shown to reduce leg volume 5
   • More effective than sitting with legs elevated 5

3. Other interventions with some evidence:

   • Reflexology may help reduce symptoms associated with edema 5
   • Rutosides (a phlebotonic) may help relieve symptoms of varicose veins, though safety data is limited 5

Common Pitfalls

• Dismissing unilateral leg swelling as normal pregnancy edema (could indicate DVT)
• Failing to recognize that foot size changes may be permanent in some women 2, 3
• Overlooking the need for properly fitting footwear to prevent pressure sores, especially in women with diabetes 3
• Assuming all edema is benign without assessing for signs of preeclampsia or DVT

Remember that while foot swelling is common and often normal during pregnancy, it should be monitored, especially when severe, sudden, or accompanied by other symptoms that might indicate complications such as deep vein thrombosis or preeclampsia.