The question of why the implanted embryos do not successfully implant has always been a question that doctors treating infertility, reproductive medicine scientists and infertility-related practitioners would like to know and discuss. The reasons for the failure of embryo implantation in IVF can be summarized as follows: 1. Decreased ability of the endometrium to accept embryos 1. Uterine structure abnormalities Uterine structure abnormalities such as congenital malformations of the uterus (bicornuate uterus, longitudinal diaphragm in the uterine cavity), endometrial polyps, endometritis and fibroids in the uterine cavity. 2. 2, thin endometrium Having had a uterine scratching procedure for abortion, irregular menstruation (persistent menstrual flow) or poor blood circulation can cause thin endometrium. 3, persistent fluid accumulation in the uterine cavity Water accumulation in the uterine cavity can be caused by edema and incompetence of the fallopian tubes, which is caused by obstruction of the umbrella (tail) of the fallopian tubes, resulting in the flow of water in the fallopian tubes to the uterine cavity. Persistent fluid accumulation in the uterine cavity can cause embryo implantation failure. However, in patients with polycystic ovarian disease, after receiving ovulation stimulation medication, fluid accumulation in the uterine cavity may occasionally occur, but it does not cause the problem of failure of implantation. 4. Adhesive proteins secreted by endometrial cells Poor quality or insufficient amount of adhesive proteins secreted by endometrial cells or too much or too little amount of certain cytokines in the uterine cavity may affect the success of embryo implantation. 5. Autoimmune disease or thrombosis It is indisputable that autoimmune disease or thrombosis is related to habitual miscarriage, but there is no definite conclusion on whether it is related to repeated embryo implantation failure. The embryo implanted in the uterus is defective. 1. Chromosomal abnormality of the couple will affect the development of the embryo, so that the embryo will stop growing at a certain stage. If the wife has chromosomal abnormalities, such as chromosomal counterbalance, chimeric chromosomes, reverse chromosome translocation, chromosomal deletion, chromosomal breakage (especially if the breakage is in the central segment of the chromosome, the chances of repeat failure of IVF will be higher even for young women). In some patients with sparse spermatozoa and poor motility, their spermatozoa were subjected to fluorescent antibody hybridization to check for normal spermatozoa chromosome count, and it was found that they had a higher percentage of abnormal sperm chromosome count than those with normal sperm count and normal motility. Repeated IVF pregnancy failure cases were found to have up to 60% of embryos with chromosomal abnormalities, so many embryos implanted in the uterus failed to implant because of chromosomal abnormalities in the embryos themselves. These chromosomally abnormal embryos sometimes appear to be of normal cell size, divide at a normal rate, and are good grade 1 or 2 embryos on the embryo classification scale. The older the woman is, the greater the chance of having an abnormal embryo. The zona pellucida, which surrounds the egg, is used to protect the egg and embryo before fertilization and before embryo hatching and implantation. If the embryo is incubated for too long in vitro, the zona pellucida will become thicker and stiffer; in older women, the zona pellucida is also thicker. If the zona pellucida is too thick or too hard, it may cause the embryo to fail to implant. 3. Poor in vitro culture environment Poor in vitro culture environment, including poor culture fluid, improper temperature or poor operating techniques, may damage the embryo and cause failure of embryo implantation.