If intercourse occurs on the day of ovulation, the fertilized egg usually begins to implant after 6-7 days, but the exact time varies from person to person. Fertilized ovum implantation includes localization, adhesion, and invasion. At the time of implantation, the disappearance of the zona pellucida, the differentiation of blastocyst trophoblast cells into syncytial trophoblast cells, the synchronized and coordinated development of the endometrium with the blastocyst, and the presence of sufficient estrogen and progesterone in the mother must be met. If one of these criteria is not met, the fertilized egg will not successfully implant. In some patients, the disappearance of the zona pellucida of the fertilized egg is late, resulting in delayed implantation, and the gestational sac may not be seen on ultrasound at about 6 weeks of pregnancy. Some patients do not have enough estrogen and progesterone in their body or due to various reasons, the endometrium can not synchronize with the development of blastocysts, and at this time, the implantation will also fail. It is recommended that women with fertility requirements should not exercise strenuously after ovulation, take proper rest, eat a light diet, and consult a doctor if they have any discomfort.