1. eggs. Eggs are stored in the ovaries as early as fetal life. 5 month old fetuses have about 7 million eggs in their ovaries, most of which will perish before she is born, with about 2 million at birth, and the decreasing rate of egg number continues until puberty when it slows down. In adolescent women, there are still between 200,000 and 500,000 eggs in the ovaries, but only 400 to 500 mature eggs. During the reproductive years, the female ovary expels eggs regularly, on average one per month. 2. Ovaries. The female ovaries are on either side of the uterus (located in the center of the pelvis, above the pelvic floor), which is covered by the umbrella of the fallopian tubes (the flared end of the fallopian tubes). The fertilized egg evolves into the yolk sac, which protects the developing embryo during the first week after fertilization. If the embryo is male, the yolk sac degenerates and evolves into the placenta; if the embryo is female, about 100 adult embryonic cells detach from the yolk sac and enter the tiny embryo along the umbilical cord, where they then approach the future ovarian tissue, “settle” and multiply rapidly. 3. Physiological cycle. In women with a stable physiological cycle, ovulation occurs about 14 days after menstruation. If the physiological cycle is more or less than 28 days, the ovulation and fertilization period will also be extended or advanced accordingly. The hormonal changes in the body of a woman of childbearing age occur in a cyclical manner from month to month, all in preparation for conception. The hormones that control the cycle are estrogen, luteinizing hormone, follicle stimulating hormone (FSH) and luteinizing hormone (LH), which stimulates ovulation when LH reaches its peak. Before ovulation, the body temperature drops and then rises. The day before the temperature drops and the day after the temperature rises is the most fertile. Cervical discharge also goes through a cycle of changes. Near ovulation, the discharge increases and is clearer, more elastic, wet and slippery, ready to receive sperm. At ovulation, a single follicle splits and expels an egg, which immediately evolves into the corpus luteum to secrete progesterone. Progesterone is the key hormone for embryonic development. If the egg is not fertilized, the corpus luteum falls back. After ovulation is over, the endometrium (uterine wall) proliferates in a spongy fashion under the combined effect of estrogen and corpus luteum to allow implantation of the fertilized egg. When the egg is not fertilized, the corpus luteum falls back and the endometrium is shed with the onset of menstruation.