First obstacle: the female reproductive tract: Sperm must pass through the vagina, cervix and into the uterine cavity before reaching the fallopian tubes, where they wait for the egg to fertilize it. Second obstacle: female ovum zygote: The zygote is a layer of granulosa cells immediately outside the ovum, which are dispersed in a gel-like hyaluronic acid, a mucopolysaccharide that can be degraded by the enzyme hyaluronidase, which is contained in the acrosome of the head of the spermatozoon and dissolves the zygote, opening the second obstacle. The third obstacle: the zona pellucida of the female egg: after the spermatozoon penetrates the oocyte and reaches the zona pellucida, the acrosome of the sperm head contains enzymes of different compositions, the most important of which is the acrosomal enzyme, with the release of sperm acrosomal enzyme the acrosomal membrane forms a lot of small holes, and at the same time, spermatozoa bind to the zona pellucida and the acrosomal reaction is activated. The acrosome reaction releases a large amount of acrosomal enzymes, which change the structure of the cell membrane of the equatorial plate of the sperm head, preparing for the fusion of the sperm and egg cell membranes in the future. Therefore, the integrity and normal morphology of the acrosome in the head of the spermatozoon is important for the mutual contact between sperm and egg. The fourth obstacle: the egg membrane of the female egg The dissolution of the zona pellucida by the acrosome of the spermatozoon requires one last obstacle – the egg membrane. The combination of the sperm and the egg leads to a series of localized changes in the egg membrane, which ultimately leads to the occurrence of a cortical response, preventing the occurrence of polyspermic fertilization. The sperm nucleus combines with the egg nucleus to form a prokaryotic nucleus, and a few hours later, a syncytium is formed, and fertilization is completed. Therefore, the pH of the vagina, the nature of the cervical mucus, the presence of anti-sperm antibodies, and the morphological integrity of the sperm acrosome are all factors that can affect fertilization.