Determination of gestational age by serum concentrations of human chorionic gonadotropin.

To examine the accuracy and predictability of human chorionic gonadotropin concentrations in determining gestational age, serum concentrations of human chorionic gonadotropin (beta-subunit) were measured during the first 157 days after last menses. Using the regression curve generated, human chorionic gonadotropin concentrations obtained during the first 60 days accurately predicted the day of gestation. The difference (mean +/- SD) between the human chorionic gonadotropin-predicted estimated date of confinement and the estimated date of confinement established by known dates of last menses was 3.1 +/- 2.3 days. In patients followed to parturition, the difference between human chorionic gonadotropin-estimated gestational age and gestational age by physical assessment of the neonate was 8.1 +/- 7.1 days. After 60 days' gestation, human chorionic gonadotropin concentrations vary widely and are of little value in predicting gestational age. In addition to documenting conception, early human chorionic gonadotropin determinations accurately date the gestation and complement other clinical and biophysical methods for determining gestational age that are frequently used later in pregnancy.