After the fertilized egg is implanted, the gestational sac can be seen by ultrasound in about 10 days at the latest, and the yolk sac can be seen inside the gestational sac, and the germ tissue can be seen by ultrasound in about half a month after the implantation, and then the primordial cardiac tube pulsation can be seen by ultrasound in about one week. Therefore, if no embryonic tissue can be seen within the corresponding time, it may be caused by abnormal embryonic development, and it is recommended to combine the results of clinical blood HCG and progesterone tests for comprehensive analysis. It is recommended not to have sex in the first three months of pregnancy, because the fetus is still unstable at this time, and if you have sex, the uterine contractions caused by sexual stimulation may result in miscarriage.