Essential to human reproduction is the egg. The egg is also the largest cell in the body and is unique to women, the mother cell that produces new life. The egg, the largest cell in the body, is produced by what is commonly referred to as the female gonad, the ovary. The main function of the ovaries, in addition to secreting essential female sex hormones, is to produce eggs. In girls, the ovaries take shape during the embryonic period at about 3 to 6 weeks of gestation. Before birth, millions of oocytes are formed in the ovary, and after childhood and adolescence, there are only 100,000 oocytes left in adulthood. The oocytes are encapsulated in the primordial follicle, and under the influence of sex hormones, only one primordial follicle matures each month, and the mature egg is then expelled from the ovary into the abdominal cavity. Generally speaking, a woman has about 300-400 mature eggs in her lifetime, and the rest of the oocytes are left to their own devices. The egg enters the fallopian tube in about 8-10 minutes after being expelled from the ovary and arrives at the point where the fallopian tube joins the isthmus (the abdomen of the fallopian tube) via the umbilical part of the fallopian tube, where it stays. If sperm is encountered, fertilization takes place here. The site of union of the human egg with the sperm is mostly in the abdomen of the fallopian tube. An egg can survive for about 48 hours after expulsion, during which time it waits to meet and unite with a sperm. If the egg is unable to meet the sperm to form a fertilized egg for various reasons, it will die naturally after 48-72 hours. If she loses this chance to be fertilized, she has to wait until another egg matures and is expelled a month later, repeating the same process. The left and right ovaries usually ovulate in turn, and in rare cases two or more eggs can be released at the same time. If they are combined with sperm separately, dizygotic twins and polygynous twins occur. Among the causes of female infertility, ovarian factors account for about 15% – 25% of infertility, and ovarian failure to ovulate is one of the important causes. During the fertilization process, sperm have to travel a long distance to complete the “kiss of life” with the egg to achieve the purpose of conception. The sperm is ejected into the vagina with the semen and travels through the cervix and uterus to the fallopian tubes where it unites with the egg to form a fertilized egg. The smoothness of this process is closely related to the mobility of the sperm and the physiological conditions of the female reproductive tract. After the contraction of the uterus and fallopian tube muscles, a large number of sperm lose their vitality and die out, so that only about 20 to 200 sperm reach the egg and only one sperm can unite with an egg. The average time for fertilization after sexual intercourse is 12 to 24 hours. Sperm enters the vagina: After semen is ejaculated into the vagina during intercourse, most of it accumulates in the posterior vaginal vault, and the cervical opening is immersed right in this pool of semen. Under normal conditions, sperm can enter the cervical canal after a few minutes. The normal vaginal environment is acidic, and this environment is physiologically important for the self-cleaning effect of the vagina, but is not conducive to sperm activity and survival. However, seminal plasma, which is a mixture of epididymis, seminal vesicles, prostate and urethral bulb gland secretions, is alkaline and can dilute and neutralize the acidic vaginal fluid. In addition, the increased secretion from the cervical fluid, which is alkaline during sexual intercourse, can turn the area around the cervical opening neutral or alkaline. All these create conditions for sperm to survive and move around in the vagina. Sperm crossing the cervix: The ability of sperm to cross the cervix is closely related to the biochemical properties of the cervical mucus, the secretion of which is directly influenced by the levels of estrogen and progesterone secreted by the ovaries. In the preovulatory period, the mature follicles secrete a large amount of estrogen, which makes the cervical mucus thin, clear and transparent like egg white, and the amount increases. It contains nutrients such as sugar, microbiotin and salts, which provide energy for sperm activity. The cervix plays a screening role for sperm, and only those sperm with normal morphology and high motility can successfully pass through the cervix. Then again, there is a substance in the seminal plasma that inhibits sperm activation and attaches to the sperm head. During the passage of sperm through the cervical mucus, these substances can be removed and insemination can be obtained, a process called energy acquisition. The spermatozoa run through the uterine cavity: After entering the uterine cavity through the cervix, the spermatozoa continue to swim upward through the uterine horn and reach the isthmus of the fallopian tube with the help of the uterine fluid. Sperm passage through the fallopian tubes: Sperm run through the fallopian tubes, mainly through brief segmental contractions of the tubal muscle wall, causing sperm and tubal fluid to flow toward the abdomen of the fallopian tubes. The epithelial cells of the fallopian tubes have numerous cilia which oscillate in the direction of the umbilical end towards the uterine cavity. The egg is released from the ruptured mature follicle and is captured by the umbilical end of the fallopian tube. The egg is not motile and its movement depends on the contraction of the smooth muscle of the fallopian tube and the oscillation of the epithelial cilia. It moves passively and slowly towards the uterine cavity where it unites with a sperm that is moving upstream and is fertilized. The fertilized egg moves passively into the uterine cavity and lays in the endometrium and a new life begins. The sperm can survive in the female reproductive tract for several days and the ability to fertilize can be maintained for 2-3 days, while the egg survives for only 1-2 days after discharge and then degeneration occurs. Therefore, if the time of ovulation cannot be accurately determined, it is easier to conceive 1-2 days earlier than after the wrong time. Only when a woman has intercourse between 3 days before and 1 day after ovulation does she have a greater chance of getting pregnant. If either party has lost the ability to fertilize by the time the sperm meets the egg, conception is not possible. In order to ensure the successful completion of fertilization, the following conditions must be met: 1. The male partner has normal sexual function and is able to ejaculate normally. 2. The male partner has sufficient sperm of normal form and function, and a fluid environment suitable for sperm to swim. 3. The female partner is able to produce normal and mature eggs, and the fallopian tubes are open. 4. Normal sexual intercourse occurs before and after the woman’s ovulation period to ensure that the sperm and egg have a chance to meet. Every life is not easy to come into this world. We should cherish life doubly. During sexual intercourse, about 300 million sperm may enter the vagina. But only one sperm may cross the many barriers to fertilize the egg and eventually create an embryo. The egg swims through the approximately 15 cm long, narrow fallopian tube toward the uterus, where it is surrounded by nutrient cells like a beautiful halo. Soon, it will meet the sperm and begin the process of fertilization.