Accuracy of Serum Human Chorionic Gonadotrophin for Estimating Gestational Age in the First Trimester of Pregnancy: Population-Based Study.

This study determined the accuracy of first-trimester serum human chorionic gonadotrophin (hCG) for estimating gestational age (GA). We included 273 584 singleton live births that had a first-trimester ultrasound and measured serum hCG at 4-12 weeks gestation in Ontario from 2012 to 2018. We estimated hCG accuracy compared to known GA, within a boundary of ± 1 week. Between 4 to 8 weeks gestation, sensitivity of hCG was over 88% and specificity over 51%. However, at 9-12 weeks gestation, sensitivity declined from 72% to 0%, and specificity rose from 86% to 100%. At all GA, the positive predictive value was consistently under 42%, while negative predictive values were over 96%. Within epidemiological studies in which GA is otherwise unknown, first-trimester serum hCG may aid somewhat in estimating GA between 4 to 6 weeks gestation, but much less so thereafter. Thus, there remains an ongoing need for an accurate method for estimating missing GA within large datasets.