If your hCG level falls over a period of two to three days in the first trimester in two quantitative hCG blood tests, this almost always means an impending miscarriage especially for a woman with other miscarriage symptoms, such as vaginal bleeding during pregnancy.
In the first trimester, hCG levels are supposed to increase over time in normal pregnancies. Usually, hCG levels should double every two to three days in early pregnancy.
Decreasing hCG levels later in pregnancy, such as the second and third trimester, are probably not a cause for concern. Most doctors do not check serial quantitative hCG levels for purposes of evaluating the progress of a pregnancy after the first trimester, although single hCG levels might be checked as a part of the AFP prenatal screening test.
Source:
American Pregnancy Association, "Human Chorionic Gonadotropin (hCG): The Pregnancy Hormone." July 2007. Accessed 17 Jan 2008.
