|Test Performed Stat
Estradiol determinations have been used for many different purposes. They have been used to investigate precocious puberty in young females and gynecomastia in men. However, its principal uses have been the differential diagnosis of amenorrhea and in the monitoring of ovulation. Under the influence of FSH, several follicles will start to develop during a normal menstrual cycle. The ruptured follicle undergoes changes and becomes known as the corpus luteum. Estradiol dominates the events during the Follicular phase and progesterone with the help of estradiol, dominates the events during the luteal phase. Early in the menstrual cycle, estrogen and progesterone are constant and low. On the other hand FSH levels are rising and LH levels are low. The high levels of FSH stimulate follicular growth and also help to stimulate the output of estradiol. By days 7 and 8, estradiol is rising at a rapid rate and reaches its peak before ovulation. When these rising levels of estradiol occur, there results a negative feedback to the hypothalamus and pituitary glands. This causes a fall in the FSH levels. The rise in estradiol triggers a rise in LH. Estradiol reaches a maximum on the day before the LH peak. During the midcycle there is a maturation of the graafian follicle due to the peak rise in LH. The follicle at this time is ruptured and the ovum is released 16 to 24 hours after the peak. Before this LH surge and ovulation, the estradiol level will drop and then rise after ovulation. The ruptured follicle, known as the corpus luteum, releases progesterone and these levels begin to rise. This causes an inhibition of the secretion of LH. Progesterone reaches its maximum in 8-9 days after the LH peak. FSH and LH decline throughout the luteal phase while estradiol and progesterone increase. As the corpus luteum regresses, estradiol and progesterone levels start to diminish. This results in the increase of FSH which stimulates the whole process over again with the growth of new follicles in the ovary.
As a result of the ovarian hormones, many changes occur in the endometrium for the implantation of the fertilized ovum. Rising estradiol levels stimulate the reconstruction of the secretory glands of the uterus, the blood vessels, and the endometrium. If fertilization does not occur the surface of the endometrium will slough off and estradiol levels will be decreased.