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When a girl is born, there are around 2 000 000 primary follicles in her ovaries, which contain immature ovarian cells. This is a huge stock. Nature has a great choice especially because of the maturity throughout child-bearing age, that is from the age of adolescence to menopause, reaches only about 400.
Preparing a particular egg for an ovulation begins three cycles earlier, when 50 to 300 follicles start to grow. After 10 weeks, only one of them reaches the stage of a dominant follicle. Others undergo atresia, i.e. overgrow or pass in to the cystic form. At the same time in the ovary we have follicles in the various stages of development (see figure).
Let’s think about 3 fundamental questions:
The answer to these questions, still bothering many, is in a complex endocrine transformation occurring in the axis: in the brain hypothalamus - anterior lobe of the hypophysis - the ovary.
First, after menstruation the hypothalamus sends a neurohormonal signal towards the pituitary gland which produces the stimulating hormone (FSH). FSH triggers a few follicles to develop into the mature eggs. One of these will develop into the dominant follicle, which will release a mature egg and the others will disintegrate. As the follicles mature they send out another hormone, estrogen. The high levels of estrogen will tell the hypothalamus and pituitary gland that there is a mature egg.
A luteinizing hormone (LH) is then released, referred to as your LH surge.
A follicle is increasing rapidly, approximately 3 mm per day, eventually reaching a diameter of 18-22 mm. Its outer layer, consisting of granular cells become extremely sensitive to the reproach of a luteinizing (LH).
In 8-38 hours after the estrogen peak, the LH reaches its peak. It is also the beginning of the secretion of progesterone. The LH surge causes the egg to burst through the ovary wall within 24-36 hours and begin its journey down the fallopian tube for fertilization.
The moment of ovulation is very limited in time, because after the decline in LH it can no longer be reached.
The cell released from the Graafian follicle retains the capacity for fertilization 12-18 hours after ovulation.
After the release of an egg cell, the cracked Graafian follicle becomes a corpus luteum secreting more progesterone. Its high level inhibits the secretion of LH and FSH, and thereby prevents the maturation of other the egg cells in the same cycle.
Because of the complexity of hormonal processes, involving a feedback mechanism, neither an additional ovulation nor an ovulation suddenly provoked by some external factor is possible.
Naturally, it happens that two dominant follicles ripen at the same time and there may be the release of two egg cells, but only at an interval of several hours, one after another.
The moment of the ovulation is not possible to observe on your own but only during the ultrasound monitoring of ovaries. The observed indicators of fertility (cervical fluid changes, cervix changes and BBT shift) do not indicate the moment of ovulation. They are, however information about the fertile period in a given cycle. A certain percentage of women note the group of typical symptoms emerging around ovulation. Among them we can find ovulatory pain, water retention in the body, constipation, acne, and sometimes breakthrough bleeding (spotting, not to be mistaken for the beginning of menses). These all are symptoms of the ongoing fertile period.
The information about the time of ovulation itself is completely unnecessary when we take into consideration everyday life – planning or postponing conception. It is more important to determine the period when the sperm cells are able to survive in the female body and reach the reproductive organs to meet the ovarian cell capable of being fertilized. This fertile period determining is the subject of studies of modern methods of natural family planning also known as the methods of fertility awareness.