What causes low HCG and missed a period?

Low hCG levels and missed period can be caused by a pregnancy that is not developing normally, such as a chemical pregnancy or ectopic pregnancy. Another common reason for low hCG levels is that the pregnancy is not as far along as estimated. This can happen if the woman ovulated later than expected or if the embryo is slow-growing. If the hCG levels are very low, it could be a sign that the pregnancy is not viable. In this case, the levels may eventually drop and the woman may experience bleeding or spotting.