Doubling times of human chorionic gonadotropin increase in early viable intrauterine pregnancies.

Although the doubling time of serum human chorionic gonadotropin has been assumed to be constant in early viable intrauterine pregnancy (prior to 6 to 7 weeks after menses), the range has varied between 1.4 and 3.5 days in the literature. To evaluate this variability of the doubling time, the mean doubling times at different ranges of human chorionic gonadotropin concentrations were determined in 49 normal pregnancies, and the doubling times at different intervals of gestation from both the day of the basal body temperature shift and the last menstrual period. The data obtained from the three different methods indicate that the doubling time of human chorionic gonadotropin is not constant but rather increases with increasing human chorionic gonadotropin concentration or gestational age. In addition, statistical analysis of the semilogarithmic plots of serum human chorionic gonadotropin concentrations indicated that the exponential rate of increase of serum human chorionic gonadotropin significantly decreases with gestational age. Since serum human chorionic gonadotropin doubling times increase and the exponential rate decreases with gestational age, estimates of normal values should be established for small sampling ranges and/or short intervals of gestation.