When blood is drawn to check for human chorionic gonadotropin after transplantation, if the value is more than 2,500 U/L, an ultrasound can be done to check for the presence of a gestational sac in the uterine cavity.
Generally, it may take about 1 week from the formation of fertilized egg to the beginning of secretion of human chorionic gonadotropin after the fertilized egg has been placed in the uterine cavity. However, due to the small size of the gestational sac, the sac cannot be seen when ultrasound is done.
As the duration of pregnancy increases, the human chorionic gonadotropin in the body will also increase gradually. Generally speaking, when the value of human chorionic gonadotropin exceeds 2500U/L, that is, when the pregnancy is about 40 days old, the pregnancy sac can usually be detected by ultrasound.
Generally, if the embryo is well developed, the doubling of the human chorionic gonadotropin value is better, but if the value is not doubled well, it indicates that the embryo is not well developed or there is an ectopic pregnancy.