It is not very accurate to know how long is the pregnancy through blood test, mainly because the normal value of blood HCG within the same pregnancy week is very big span. If you want to know how far along the pregnancy is, it is best to measure the size of the gestational sac through ultrasound, or the following can be referred to: 1. If you are 5 weeks pregnant, basically through ultrasound you can see the yolk sac. 2. If you are 6 weeks pregnant, through ultrasound you can see the embryonic tissue. 3. If you are 7 weeks pregnant, through ultrasound you can see the primordial cardiac tube pulsing. The vast majority of pregnancy will have these manifestations, is not absolute, but also to analyze the specific circumstances.