What change occurs in the total lung volume during pregnancy?

During pregnancy, the total lung volume actually decreases, primarily due to the elevation of the diaphragm as the uterus expands. As the growing fetus occupies more space within the abdominal cavity, the diaphragm is pushed upwards. This change results in a reduction in the vertical space available for the lungs to expand fully, which leads to a decrease in total lung volume.

Additionally, while there may be an increase in the tidal volume and inspiratory reserve volume as a result of hormonal changes and the body's increased oxygen demands, these changes do not offset the overall decrease in total lung volume caused by the elevated diaphragm.

Recognizing these physiological changes is crucial in maternal-fetal medicine, as they can influence respiratory function and have implications for both maternal and fetal well-being throughout the course of pregnancy.