Severe tachypnoea and dyspnoea due to physiological hyperventilation in pregnancy

Physiological hyperventilation and dyspnoea in pregnancy are well-established phenomena and commonly lead to a chronic respiratory alkalosis with compensatory renal excretion of bicarbonate. However, the underlying mechanism of dyspnoea during normal pregnancy remains largely undefined. Increasing progesterone levels are a primary factor leading to increased respiratory drive to ensure the rising metabolic demands of the pregnancy are met. Dyspnoea symptoms typically begin in the first or second trimester, are mild, and do not interfere with activities of daily living. We report the case of a 35-year-old female with severe physiological hyperventilation of pregnancy presenting with profound dyspnoea, tachypnoea, and presyncope from 18 weeks of gestation until delivery. Subsequent investigations revealed no identifiable underlying pathology. There remain limited reports of such severe physiological hyperventilation of pregnancy. This case highlights interesting questions regarding the respiratory physiology of pregnancy and underlying mechanisms.