During which period of pregnancy does maternal blood pressure typically decrease the most?

Maternal blood pressure typically decreases the most during the second trimester of pregnancy. This decrease is primarily due to the effects of hormonal changes and the expansion of blood volume. As pregnancy progresses, particularly during the first and second trimesters, there is an increase in levels of progesterone, which causes vasodilation. This vasodilation leads to a reduction in systemic vascular resistance, allowing blood vessels to expand and accommodate the increased blood volume needed for the developing fetus.

Furthermore, the growing uterus exerts pressure on the inferior vena cava, especially when the mother is in a supine position, which can contribute to changes in hemodynamics. However, the most significant and consistent decrease in maternal blood pressure is observed during the second trimester when the body is adapting to the demands of the growing fetus while still managing the physiological changes that occur.

By the third trimester, maternal blood pressure tends to stabilize or even increase slightly as the body prepares for labor and delivery, while during labor, there can be various physiological and stress-related factors that may also influence blood pressure, but these circumstances do not lead to a sustained decrease as seen in the second trimester.