Pregnancy and breathlessness

Elevated serum progesterone levels stimulate respiratory drive and lead to an increased tidal volume and raised minute ventilation, with only a modest increase in O2 consumption. Any cause of maternal hypercapnia leads quickly to foetal respiratory acidosis. Elevation of the diaphragm occurs due to the enlarging uterus, leading to a reduced functional residual capacity (FRC). Raised levels of coagulation factors and impaired fibrinolysis, combined with venous stasis, result in a significantly increased risk of venous thromboembolism (VTE). Upper airway oedema, particularly in the setting of pre-eclampsia, may predispose to upper airway obstruction during sleep, but rarely frank OSA. OSA tends to occur in obese women and may be associated with impaired foetal growth and pre-eclampsia. Snoring in pregnancy is a poor predictor of OSA.