Respiratory changes during pregnancy

The shape of chest changes because uterus enlarges. The diaphragm
is elevated as much as 4cm and rib cage displaced upwards.

Que. -  How it can possible to transfer of oxygen (O2) from mother to fetus ?
Ans. -  There is progressive increase in oxygen consumption which is caused
            by the increased metabolic need of mother and fetus. The hyperventilation
            causes change in acid base balance.The arterial PaCO2 falls from
            38 to 32 mm Hg and PaO2 from 95 to 105 mm Hg. This facilitate
            transfer of CO2 from the fetus to the mother and O2 from the mother
            to the fetus.

Changes in the respiratory system -

	Non     Pregnant	Pregnancy   Near term	Changes
Respiratory rate             (per min)	15	15	Unaffected
Vital capacity                 (ml)	3200	3300	Increased
Tidal volume               (ml)	475	675	+40%   Increased
Residential  volume                 (ml)	965	765	-20%   Decreased
Total lung capacity                (ml)	5000	4750	-5%     Slightly   decreased