The reasons for late implantation of blastocysts may be the late formation of fertilized eggs, long fallopian tubes in women, as well as irregular menstruation, inflammation of the fallopian tubes, and poor uterine environment in women. 1. Late fertilization: the time of blastocyst implantation is closely related to the time of fertilized egg formation. When the time of blastocyst implantation is late, it is necessary to consider that the combination of sperm and egg is late, which leads to the delay of blastocyst formation. Late blastocyst implantation due to late formation of fertilized egg can be considered as a normal physiological phenomenon. 2. Long fallopian tube: As the blastocyst still needs to move gradually from the fallopian tube to the endometrium before it can be implanted in the uterus. Therefore, if a woman’s fallopian tube is long, it will lead to prolonged traveling time of blastocysts, thus forming the phenomenon of late implantation. For the phenomenon of long fallopian tubes, regular ultrasound examination of the uterus is enough and no special treatment is needed for the time being. 3. In addition, irregular menstrual cycle and delayed ovulation of ovary, which prolongs the formation of fertilized egg, will also lead to late implantation of blastocyst. Inflammation of the fallopian tube or poor uterine environment, such as inflammation, fibroid tumor, etc. may also affect blastocyst implantation. After the phenomenon of late implantation of blastocysts, women are advised to go to the hospital in time for obstetric examination and ultrasound, to verify the gestational week and to have regular obstetric examinations.