Ventilation in pregnancy

Ventilation begins to increase significantly around 8 weeks of gestation.
Mechanical aspects of ventilation alter significantly in pregnancy.
Tidal volume increases about 40% (from 500ml to 700ml). The respiratory rate remains unchanged. Therefore the minute ventilation (the amount of air in and out of the lungs within one minute) increases. That minute volume is the product of tidal volume and the respiratory rate. It increases by approximately 30-50% with pregnancy.
Pregnant women perceive this increase in minute volume as shortness of breath, which affects 60-70% of pregnant population.
Expiratory reserved volume and residual volume both decrease in pregnancy. The sum of these two, the functional residual capacity, decreases about 10-25%. FRC is further reduced in supine position.
Forced expiratory volume in one second FEV1 and peak expiratory flow rate remain unchanged.