Final answer:
During menses, the estrogen levels in the blood are lower than at ovulation. Estrogen levels peak prior to ovulation, triggering the release of an egg, but decline during menses when the uterine lining is shed.
Step-by-step explanation:
The amount of estrogen in the blood during menses is lower compared to the amount of estrogen at ovulation. Estrogen levels rise substantially leading up to ovulation, which occurs around day 14 in a typical 28-day menstrual cycle.
This estrogen surge triggers a luteinizing hormone (LH) surge that results in the release of an egg from the ovary. Conversely, estrogen levels are generally lower during menses, when the lining of the uterus is shed at the beginning of the menstrual cycle. This is because the corpus luteum, which produces estrogen, has degraded, leading to a decline in estrogen levels.