A drop in HCG in the blood at 8 weeks of pregnancy is an abnormal condition. HCG is still elevated at this time, but the increase will be slower than when you first became pregnant. Because the HCG doubles within 2 days when you are first pregnant, the HCG in the blood will continue to rise at 8 weeks of pregnancy, but it will not double immediately in 2 days. Normally, the HCG in the blood decreases slowly until the 10th week of pregnancy, and the HCG in the blood is about 1/10th of the highest value when the baby is delivered in the hospital. Therefore, if the HCG in the blood drops at this time, it may be caused by the poor development of the embryo or inevitable miscarriage, and an ultrasound should be done as soon as possible to clarify.