What are the primary physiological changes that occur during pregnancy?

The primary physiological changes that occur during pregnancy include increased blood volume, elevated heart rate, and hormonal shifts. During pregnancy, a woman's blood volume can increase significantly, often by 30-50%, to supply nutrients and oxygen to the developing fetus and to accommodate the changes in circulatory demands. This increase can lead to a corresponding rise in heart rate as the heart pumps more blood to support the growing baby and the mother's body.

Additionally, there are substantial hormonal changes that play essential roles in supporting pregnancy. Hormones such as progesterone and estrogen increase, which help maintain pregnancy, prepare the body for childbirth, and influence various metabolic processes.

The other options do not accurately reflect the physiological changes associated with pregnancy. Increased muscle mass and heightened immunity may not be universally experienced during pregnancy, and in many cases, women may experience fatigue. Additionally, decreased blood pressure and lower heart rate do not characterize pregnancy, as these metrics typically fluctuate in the opposite direction. Lastly, an increase in respiratory rate often occurs, but decreased appetite and weight loss are generally not typical during pregnancy, as many women experience an increase in appetite as their bodies require additional calories to support fetal growth.