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At menopause, only 1,000 follicles remain. It seems likely that early menopause occurs for women with low populations at birth, and late menopause occurs for women with high populations at birth, but there is as yet no clinical evidence for this. [4] The process by which primordial cells 'wake up' is known as initial recruitment.
Cycles in which ovulation does not occur (anovulation) are common in girls who have just begun menstruating and in women around menopause. During the first two years following menarche, ovulation is absent in around half of cycles. Five years after menarche, ovulation occurs in around 75% of cycles and this reaches 80% in the following years. [62]
Menopause, also known as the climacteric, is the time when menstrual periods permanently stop, marking the end of reproduction. [1] [6] [7] It typically occurs between the ages of 45 and 55, although the exact timing can vary. [8] Menopause is usually a natural change related to a decrease in circulating blood estrogen levels. [3]
Ovulation is an important part of the menstrual cycle in female vertebrates where the egg cells are released from the ovaries as part of the ovarian cycle. In female humans ovulation typically occurs near the midpoint in the menstrual cycle and after the follicular phase. Ovulation is stimulated by an increase in luteinizing hormone (LH).
Menopause results from having too few ovarian follicles to produce enough estrogen to maintain the ovarian-pituitary-hypothalamic loop, which results in the cessation of menses and the beginning of menopause. Human females are born with approximately a million oocytes, and approximately 400 oocytes are lost to ovulation throughout life. [32] [33]
Usually, ovulation occurs in one of the two ovaries releasing an egg each menstrual cycle. The side of the ovary closest to the fallopian tube is connected to it by infundibulopelvic ligament, [3] and the other side points downwards attached to the uterus via the ovarian ligament. Other structures and tissues of the ovaries include the hilum.
The short-term drop in steroid hormones between the beginning of the LH surge and the event of ovulation may cause mid-cycle spotting or bleeding. [12] Under the influence of the preovulatory LH surge, the first meiotic division of the oocytes is completed. The surge also initiates luteinization of thecal and granulosa cells. [4]
Following a complete fertility workup, the first line of treatment for anovulatory infertility secondary to FHA is pulsatile exogenous GnRH followed by gonadotropin therapy and induction of ovulation when GnRH is unavailable. [9] [25] this therapy is recommended for avoiding multiple gestation and severe ovarian hyperstimulation syndrome. [1]