Changes in the respiratory system in pregnancy:
Changes in respiratory system during pregnancy:

With the enlargement of the uterus, specially in the later months, there is elevation of the diaphragm by 4 cm.
Total lung capacity is reduced by 5% due to this elevation.
Breathing becomes diaphragmatic. Total pulmonary resistance is reduced due to progesterone effect.
The subcostal angle increases from 68° to 103°, the transverse diameter of the chest expands by 2 cm and the chest circumference increases by 5–7 cm.
 A state of hyperventilation occurs during pregnancy leading to increase in tidal volume and therefore respiratory minute volume by 40%.
Vital capacity is increased
Subcostal angle remains unchanged
Tidal volume remains unaltered
Residual volume is decreased