When the sperm and egg unite, a fertilized egg is formed and life begins. However, the failure of fertilization also affects the woman’s conception. The following reasons affect embryo fertilization 1. The fertilized egg itself has defects due to its chromosomal system abnormalities, for example, the normal human individual karyotype is 46,xx (female), 46,xy (male), if the fertilized egg karyotype is 47,xxy, then the fertilized egg cannot develop normally into a normal individual, which is a fertilization failure. The more advanced the couple is, the higher the chance of having abnormalities in the fertilized egg. This explains why the eggs can be retrieved and the embryos can be formed, but the embryos just don’t clone in the IVF for advanced couples. The success rate is obviously lower than that of young couples, mainly because of the increased probability of chromosomal abnormalities in the embryo. 2. Uterine factors The failure of fertilization of fertilized eggs is most likely due to uterine dysplasia, submucosal fibroids, adenomyoma, endometrial polyps, uterine adhesions, endometrial tuberculosis, etc. As well as pelvic factors: the presence of fluid in the fallopian tubes and chocolate cysts in the pelvic cavity can destroy the pelvic microenvironment required for fertilization of the egg, which can also affect embryo implantation. 3. Immunological factors Recent studies on immunological factors have revealed that there are two types of immunological conditions that affect conception. Homoimmunity Sperm, seminal plasma or fertilized eggs are antigenic substances that are absorbed by the vagina and uterine epithelium and produce antibody substances through immune reactions, making it impossible for sperm and eggs to unite or for fertilized eggs to implant. 5. Autoimmunity It is believed that the presence of autoantibodies to the zona pellucida in the serum of infertile women can prevent sperm from penetrating the egg after reacting with the zona pellucida, thus preventing fertilization. Insufficient progesterone secretion in women and abnormalities in their endometrium can affect the fertilization of eggs. 7, excessive mental tension Especially severe anxiety and excessive psychological stress due to lack of pregnancy. The body will secrete norepinephrine and many other factors that are not conducive to embryo implantation, which affects the embryo implantation. The conception of new life is a complex physiological process, which must be combined with normal sperm and egg. We often encounter the situation of fertilization failure in the process of IVF, for which we need to understand the reasons for fertilization failure and treat the symptoms, so that we can continuously improve the fertilization rate and increase the success rate of pregnancy.