At what number of weeks into pregnancy can a woman's resting heart rate begin to increase?

During early pregnancy, physiological changes begin to occur that affect a woman's cardiovascular system. Around 2 to 5 weeks into pregnancy, hormonal changes, particularly the increase in progesterone, lead to an increase in blood volume and cardiac output. This increase can cause a woman's resting heart rate to rise as the body begins to accommodate the needs of both the mother and the developing fetus.

Additionally, as early as the sixth week, the body prepares for the physical demands of pregnancy, and this can include changes in heart rate as the circulatory system adapts. However, the most pronounced changes in resting heart rate typically start to occur at the 2 to 5-week mark, providing a clear physiological response to the onset of pregnancy. This timing aligns with early hormonal signals that facilitate these cardiovascular adjustments in preparation for the pregnancy.