1, male testes – produce normal sperm The normal adult male ejaculate volume is 2-6ml, the number of sperm in each ml of semen should be more than 20 million, the active sperm should (a + b level) reach more than 50%, the normal form of sperm is more than 4%. 2. Female ovaries – discharge mature oocytes There are only 400-500 follicles that can develop and mature during a woman’s lifetime. A few days before menstruation, follicles begin to develop. Starting from 7-8 days of the menstrual cycle, about 20 follicles begin to grow and one of them becomes the dominant follicle. The dominant follicle has the ability to develop and mature on its own while inhibiting the growth of other follicles, causing them to shrink, atrophy and disappear. In a woman with a normal menstrual cycle, only one mature oocyte is usually expelled per menstrual cycle. Intercourse around the time of ovulation is the only way to have a chance of conception. In women with normal menstrual cycles, ovulation occurs about 14 days before the next menstrual period. 3, the reproductive tract is open The male vas deferens is open so that sperm can be ejected through the reproductive tract. The female reproductive tract must also be open for the sperm to be fertilized by the egg through the fallopian tube and for the fertilized egg to return to the uterine cavity for implantation. 4. Synchronization of endometrial and fertilized egg development After fertilization, the oocyte moves toward the uterus through the oscillation of the fallopian tube cilia, during which it divides into an embryo, which reaches the uterine cavity 3-4 days later and begins to implant in 6-8 days. If the fertilized egg enters the uterine cavity earlier or later, the endometrium will not be suitable for the fertilized egg and implantation may fail and conception may not occur.