If David’s test is strongly positive, the blood HCG will basically exceed 100mIU/mL to show a strong positive result. In clinical practice, you can monitor the change of blood HCG to know whether the embryo is developing normally and whether the possibility of ectopic pregnancy is ruled out. If the blood HCG can double up every other day, it clinically indicates that the embryo is developing well and the possibility of intrauterine pregnancy is high. In case of ectopic pregnancy, the blood HCG will not double in the next day, but only rise a little, which should be taken seriously clinically. It is recommended that in the absence of clinical symptoms, such as no lower abdominal pain and no vaginal bleeding, it is best to have an ultrasound examination around 45-50 days of pregnancy to know the size of the gestational sac and to determine intrauterine pregnancy.