During the luteal phase of the ovarian cycle, progesterone secretion peaks and estrogen levels decrease. along with these changes, there is a corresponding increase in a woman's basal body temperature. In this phenomenon, it is not the increase in progesterone, but the decrease in estrogen that may signal an increase in overall body temperature. This is because the decrease in estrogen reduces the negative feedback signal to the hypothalamus, the thermoregulator for the body. The result is an increase in overall basal body temperature.