Reliability of serial urine HCG as a biomarker to detect early pregnancy loss

Background: To examine the reliability of HCG as a biomarker for early pregnancy loss, five experienced researchers independently assessed data from 153 menstrual cycles, determining whether each cycle represented,no conception,' a 'continuing conception' or a 'conception lost.' Methods: Urine samples were analysed by immunoradiometric assay using a combination of capture antibodies for the intact heterodimer (B109) and for an epitope common to the beta subunit and the beta core fragment (B204). For each cycle, HCG data were presented as graphs of daily assay results. Summary statistics for HCG assays from 46 women who had undergone bilateral tubal ligation represented baseline values. Results: Pairwise agreement among the assessors for any of the three options ranged from 78-89%. At least three experts agreed for 147 cycles (96%), accounting for 28 conception losses and 19 continuing conceptions. The multi-rater kappa was 0.62 for the conception lost category and 0.68 for continuing conceptions, indicating substantial agreement. Conclusion: The main sources of disagreement involved deciding whether there was sufficient information for assessment, interpreting cycle parameters such as cycle length or bleeding event, and interpreting a distinct HCG rise pattern that does not exceed the baseline value obtained from the sterilized women.