Respiratory physiological changes in pregnancy

Pregnancy induces a wide range of physiological changes in the respiratory system that significantly affect pulmonary function and gas exchange. These changes are mediated by both mechanical factors—such as the expanding uterus and elevation of the diaphragm—and hormonal influences, particularly from progesterone, estrogen, relaxin, and prostaglandins. Progesterone and estrogen increase minute ventilation and reduce arterial PaCO₂, while relaxin enhances ligamentous flexibility, allowing ribcage expansion to accommodate the growing fetus. Anatomical adaptations, including diaphragm elevation and an increased subcostal angle, begin early in gestation and peak in the third trimester. Lung volumes are altered, with a notable decrease in functional residual capacity (FRC) and an increase in inspiratory capacity (IC). Despite these changes in thoracic mechanics, spirometric measures such as FEV₁ and FVC typically remain unchanged. These respiratory adjustments often result in symptoms like exertional dyspnea and predispose individuals to conditions such as obstructive sleep apnea and pulmonary edema. During labor, hyperventilation can be further exacerbated by pain and anxiety. Distinguishing these normal physiological adaptations from serious pathologies—such as pulmonary embolism, peripartum cardiomyopathy, and preeclampsia—is critical for accurate diagnosis and appropriate management. This review provides a comprehensive synthesis of current knowledge while offering a unique perspective by integrating hormonal and mechanical drivers of change, mapping their evolution across gestation, and linking them to real-world clinical implications. These insights aim to support clinicians in optimizing respiratory care during pregnancy, labor, and the postpartum period.