Anovulation is the absence of the release of a mature egg (ovum) from the female ovaries. In certain cases, a woman may have one anovulatory menstrual cycle and then go back to a regular ovulatory cycle. In other cases however, anovulatory menstrual cycles occur over a long period of time. When anovulation happens, a woman cannot get pregnant. This is because no mature egg is released for sperm cells to fertilize, following unprotected sexual intercourse. For women who have completed menopause, this is quite normal. Women of childbearing age do not usually experience anovulation unless something has disrupted the body’s hormone levels or damaged the ovaries.
To have proper understanding of anovulation, the normal ovulatory cycle though a bit complex, will need to be discussed.
MENSTRUAL CYCLES AND OVULATION
Menstruation is the cyclic, orderly sloughing(shedding) of the lining of the womb , in response to interplay of hormones produced by parts of the brain: the Hypothalamus and the Pituitary gland, as well as the Ovaries (female gonads). The menstrual cycle comprises two major phases: Follicular and Luteal phase. The menstrual cycle length is the number of days between the first days of menstrual bleeding of one cycle to the beginning of the menstrual bleeding of the next cycle. The average menstrual cycle length is 28 days with most cycle lengths between 21 to 35 days.
The menstrual cycle is controlled by 4 major hormones, called Gonadotropins: Follicle stimulating hormone (FSH) and Luteinizing hormone (LH) produced by the Pituitary gland, Estrogen and Progesterone produced by the ovaries. The hormone Prolactin however, has a role in the menstrual cycle by inhibiting the production of FSH. The secretion of these gonadotropins is controlled by Gonadotropin-releasing hormone (GnRH) secreted by the hypothalamus in the brain.
In this phase, preparation of the egg to be released begins. During the period, the pituitary gland (a small area at the base of the brain that makes hormones) produces a hormone called follicle stimulating hormone (FSH). FSH tells the ovaries to begin the growth of an egg which will be released from the ovary in a process called ovulation. Throughout the menstrual cycle, there are multiple follicles (fluid filled sacs containing eggs) in each ovary at different stages of development. Halfway into the follicular phase, one follicle in one of the ovaries is the largest of all the follicles. This becomes the dominant follicle and is the one prepared to be released at ovulation. The dominant follicle produces estrogen in the ovary as it grows. Estrogen is at its highest level just before ovulation happens. For most people, the follicular phase lasts between 10 and 22 days, but this length varies from cycle-to-cycle.
About midway through the cycle, the two phases of the ovarian cycle (the Follicular phase and the Luteal phase) is divided by ovulation.
Ovulation occurs as a result of the combined actions of the hypothalamus, pituitary, and ovary. The hypothalamus releases gonadotropin releasing hormone (GnRH), which leads to the subsequent release of LH and FSH from the pituitary gland, which then act on the dominant ovarian follicle. LH levels surge just before ovulation, signaling the most fertile period of a female’s menstrual cycle. As a result of the LH surge, an egg is released from the ovary into the fallopian tube attached to the uterus (womb).Ovulation occurs usually about 13-15, in most averages 14 days before the start of the next period.
This is the phase from ovulation until the start of the next period. The sac present in the dominant follicle that contained the egg produces estrogen and progesterone in the ovary. After ovulation, the follicle that contained the egg transforms into something called a corpus luteum and begins to produce the hormones, progesterone and estrogen. Progesterone levels peak about halfway through this phase. The hormonal changes of this phase are associated with common premenstrual symptoms that many people experience, such as mood changes, headaches, acne, bloating, and breast tenderness.
If an egg is fertilized, progesterone produced by the corpus luteum supports the early pregnancy. If fertilization does not occur, the corpus luteum will start to break down between 9 and 11 days after ovulation. This breakdown results in a drop in estrogen and progesterone levels, which causes the menstrual bleeding to begin. The luteal phase typically lasts about 14 days,however, a range between 9 and 16 days is common. The end of this phase marks the beginning of menstrual bleeding which lasts for about 3-7 days. The onset of bleeding also signifies the beginning of another menstrual cycle.
CAUSES OF ANOVULATION.
Obesity causes infertility, by impairing ovarian follicular development. Obesity affects the regulation of gonadotropin (estrogen) production, causing increased free estrogen levels due to increased conversion of androgens (male hormones) to estrogens in fat tissues. Increased estrogen causes a decrease in gonadotropin-releasing hormone (GnRH) by signaling to the brain to stop its production. This, anomaly causes irregular or anovulatory cycles.
Overweight and obese women have a higher incidence of menstrual dysfunction and anovulation………………….to be continued next week