Decline of serum human chorionic gonadotropin and spontaneous complete abortion: defining the normal curve.

OBJECTIVE: We sought to estimate a standard curve of serum human chorionic gonadotropin (hCG) decline that characterizes spontaneous abortion.
METHODS: Data were extracted from a clinical database of women with symptomatic early pregnancies and nondiagnostic ultrasonography who required follow-up with serial hCG levels. The evaluation was restricted to women who had a pregnancy of unknown location, a decrease in serum levels, and who were ultimately diagnosed with miscarriage (a decrease in serum hCG to < 5 mIU/mL in the absence of surgical intervention or confirmation of products of conception after dilation and curettage). The starting point of the curve was the hCG concentration at presentation, with serial levels plotted until the time of definitive diagnosis. Semiparametric statistical techniques were used to characterize the shape of the curve. We present slopes for the decrease in log hCG levels and the projected rate of fall.
RESULTS: Of the 1,543 patients, 710 were diagnosed with miscarriage. A quadratic curve for log hCG with a steeper rate of decline for large initial hCG values best described the pattern of change. One curve could not fully estimate the decline because the rate was dependent on the initial hCG level. In other words, more rapid decline was associated with a higher starting concentration. The rate of decline ranged from 21% to 35% at 2 days and 60% to 84% at 7 days, depending on initial hCG value.
CONCLUSION: The rate of hCG decrease in spontaneous abortions is described by a quadratic profile, with a faster decline in hCG value with higher presentation levels. A rate of decline less than 21% at 2 days or 60% at 7 days suggests retained trophoblasts or an ectopic pregnancy.