Dyspnea in Late Pregnancy

Physiological Mechanisms Explaining the Paradox

Oxygen consumption rises 20-33% above baseline by the third trimester due to increased metabolic demands of the fetus, placenta, and maternal organs, creating a physiological stress on the respiratory system 1, 2
Functional residual capacity decreases by 10-25% as the enlarging uterus elevates the diaphragm, reducing the oxygen reservoir available during periods of increased demand 1, 2
The combination of reduced functional residual capacity and increased oxygen consumption creates rapid oxygen desaturation in response to any hypoventilation or apnea 1, 2
Minute ventilation increases 20-40% above baseline by term, driven by progesterone-mediated increased respiratory center sensitivity 1, 2, 3

Mild exertional dyspnea with normal physical examination requires only reassurance at 36 weeks gestation, and patients should maintain moderate-vigorous physical activity and not restrict exercise based on mild symptoms alone 4
Severe dyspnea at rest, chest pain, syncope, hemoptysis, or palpitations mandate urgent workup, and oxygen desaturation, tachypnea at rest, persistent tachycardia, abnormal lung sounds, or unilateral leg swelling require further investigation to exclude pulmonary embolism 4
Perform bilateral lower extremity compression ultrasound if pulmonary embolism is clinically suspected, and obtain chest X-ray and arterial blood gas for risk stratification 4