The most accurate test for pregnancy is to check the chorionic gonadotropin level in the blood, and if it is elevated, pregnancy is confirmed. In the early stages of pregnancy, the chorionic gonadotropin level in the blood doubles within 48 hours. If it does not double normally, there is a possibility that the pregnancy is abnormal, that it is a preterm miscarriage, an ectopic pregnancy, a biochemical pregnancy, or that the embryo has stopped developing and further tests must be done. If you are pregnant for more than 40 days, you should see a gestational sac when you have an ultrasound. If you cannot see a gestational sac, you should be highly suspicious if there is a possibility of ectopic pregnancy and you can do further tests.