Folliculogenesis is a cyclic process that occurs in the ovaries under the control of the nervous and endocrine system. Its main mechanism is the transformation and transformation of the follicle into a mature egg.
The main stage of folliculogenesis is the formation of a dominant (main) follicle.
The dominant follicle is formed by successive stages:
- the beginning of the formation of many small antral follicles ,
- the growth and development of small follicles,
- maturation of the dominant follicle,
- ovulation.
We can say that a mature dominant follicle is an egg, which should advise. Thus, it becomes clear that in the presence of all of the above stages of follicle formation, ovulation finally occurs, i.e. pregnancy is possible.
The formation of small follicles begins from the first days of the menstrual cycle. However, their growth begins only in the hormone-dependent stage, which occurs immediately after the completion of the luteal phase. Then the amount of estradiol and progesterone decreases, but the amount of follicle-stimulating hormone (FSH) increases.
It should be noted that the dominant follicle is influenced by many factors that can lead to its death. However, the female body is designed so that all its processes are aimed at preserving the egg and its fertilization. Therefore, the dominant follicle is “protected” by the epidermal growth factor and transforming growth factor (TGF).
5-7 days after the onset of menarchy, small follicles begin to form. They are also called tertiary or antral. There are a fairly large number of them - about 10 pieces. This phase of folliculogenesis is called early proliferation or the beginning of the formation of small antral follicles . The diameter of these small formations does not exceed 5 mm. They are located in the form of "beads" on the periphery of the ovary. For some time, part of the follicles increases in size and is gaining strength.
Consequently, a dominant follicle forms after about 10 days of the menstrual cycle, and at this time its size reaches 15 millimeters. Other follicles, which could not gain the required mass, regress and die. As a result, we can conclude that there can be more than one dominant follicle. When two or more eggs mature, which subsequently fertilize, a multiple pregnancy develops. This process is not common, but such cases have been recorded. Most often, this is an iatrogenic cause: hormone-based drugs, oral contraceptives or IVF. But the physiological reason for the appearance of twins and triplets is not excluded.
By the immediate moment of ovulation, the dominant follicle should reach a diameter of about 20 millimeters (maybe more). In place of the follicle, a yellow body should be formed a little smaller than its predecessor.
If fertilization does not occur, then within a week after the egg leaves the ovary, the corpus luteum begins to decrease in size - it regresses. By the time of rejection of the uterine endothelium, the corpus luteum, as a rule, dies, and in its place can only remain a site of impaired echogenicity.
Speaking of folliculogenesis, one can not stop at the concept of "persistent follicle."
Persistent is called the follicle that goes through all stages of folliculogenesis, except for direct ovulation. What reasons can lead to this phenomenon is not fully understood. However, doctors often take persistence as a variant of the norm, unless, of course, it is not constantly repeating.
Sometimes it happens that a persistent follicle turns into a small ovarian cyst. Patients with a cyst should be monitored. If this process does not cause complaints, then treatment is not required.
As a rule, persistent follicles rupture during ovulation, but it is almost impossible to get pregnant in this situation, because the uterine endometrium is too thin for implantation.