After a woman is pregnant, her blood β-hCG level can be increased from the 9th-11day, and then it can be increased twice every two days. If the rising speed is slow for two consecutive times, it may be caused by ectopic pregnancy, abnormal embryo or intrauterine growth retardation.
However, if the abnormal pregnancy is hydatidiform mole, the serum hCG concentration is much higher than the corresponding monthly value in normal pregnancy, so this difference can be used as an auxiliary diagnosis of hydatidiform mole, usually in the first 3 months of pregnancy.