The female germ cells are called oocytes. They are the largest cells in the organism – a trained eye can see them even without a microscope.
The process of egg formation is called oogenesis. All of a woman’s eggs are produced during her fetal development, i.e. before she is born. The maximum number of oocytes is reached around the 20th week of the development of the ovaries of a female baby; after that, the total number of oocytes decreases sharply. By the time a girl is born, there are only 1 – 2 million eggs left (see graphic).
Medical illustration of Bailey mariner
The number of oocytes decreases continuously with age. The decline in egg count and quality accelerates, especially after the age of 35. When the number of eggs reaches a certain threshold, spontaneous pregnancy becomes very unlikely and the woman becomes infertile. In the further course of egg degradation, the menstrual cycle ultimately stops and the woman enters menopause.
Note: subfertility and imminent infertility as a result of a decrease in egg count begin much earlier than menopause (menopause – a woman’s last menstrual cycle).
Note: For some women, the decline in fertility begins even earlier and progresses even faster than usual. At the average age at which the average woman’s fertility decline begins (35 years), these women may already be completely infertile.
