During the third trimester of pregnancy, which physiological change is NOT typically observed?

During the third trimester of pregnancy, a decrease in the leukocyte count is not a typical physiological change. In fact, it is common for the leukocyte count to increase due to various factors including hormonal changes and the body's preparation for potential infection during labor. The increase in leukocytes is part of the normal immune system adaptation during pregnancy.

The other options reflect typical physiological changes that occur during the third trimester. For instance, a decrease in PaCO2 is often observed as a result of increased minute ventilation due to the influence of progesterone, which leads to a state of respiratory alkalosis. Reduced gastric emptying rate is also common, as the growing uterus exerts pressure on the stomach, influencing digestive processes. Additionally, diminished residual lung volume occurs because the upward displacement of the diaphragm reduces lung capacities, including total lung volume and functional residual capacity.

Understanding these physiological adaptations is essential for healthcare providers in managing both the maternal and fetal aspects of pregnancy during this critical period.