Crown-rump length and serum human chorionic gonadotropin as predictors of gestational age.

The accuracy of fetal crown-rump length measurement and maternal serum human chorionic gonadotropin (hCG) concentration in the prediction of obstetric gestational age was analyzed in a study population of 77 patients for whom time of ovulation was reliably determined. Published nomograms relating maternal serum hCG concentration to gestational age were not found to be valid predictors of gestational age for the study population. Fetal crown-rump length measurement using the uncorrected regression equation of Robinson was found to give the most accurate prediction of gestational age.