The rise in minute ventilation and fall in FRC should theoretically result in a faster rise in maternal end-tidal oxygen concentration with pre-oxygenation. There is some evidence this occurs in practice.

The figure shows the rate of rise of end-tidal oxygen concentration (P_ĖO₂) in pregnant and non-pregnant subjects as predicted by physiological modelling.

McClelland SH , Bogod D and Hardman JG. Anaesthesia 2007; 63(3):259-263

Three minutes tidal breathing is the recommended pre-oxygenation strategy in pregnancy.