Human chorionic gonadotropin increase in normal early pregnancy.

Serial determinations of human chorionic gonadotropin have been used in evaluating early pregnancies. This has been based on linear regression of logarithm-transformed hCG levels. However, these levels are changing in a curvilinear fashion as pregnancy advances. Consequently the simple linear model does not provide a good fit to the data. To define more precisely the normal values for hCG increase, serial determinations were performed on serum samples obtained from 29 patients who were carrying normally advancing pregnancies. Gestational age was established with basal body temperature records. Three gestational age periods were identified each with a linear increase in hCG. This was translated into hCG doubling times and percentage increase over time. These tables may be used to determine if an early pregnancy is advancing normally.