A need exists for broadly applicable biomarkers of pregnancy outcome in population-based studies that assess environmental hazards to human reproduction. Previous studies have demonstrated that during the periimplantation period, measures of the circulating levels of immunoreactive hCG (IhCG) are not predictive of pregnancy outcome, whereas measurements of the circulating levels of bioactive hCG (BhCG) provide information relating to pregnancy outcome and might provide the basis for an early biomarker of pregnancy outcome. However, for this biomarker to have broad application in population-based studies, it must be adapted to urinary hCG metabolites. The principle objective of the present study was to characterize the periimplantation excretion patterns of urinary hCG metabolites of pregnancies that resulted in live birth (LB), early pregnancy loss (EPL), and recognized clinical abortion (CAB) with an immunoenzymometric assay specific to intact hCG and an LH/chorionic gonadotropin cellular bioassay as the basis for a preliminary comparison between successful (LB) and failing (EPL and CAB) outcome groups. Automated immunoassays for FSH and hCG were used to define each conceptive cycle's implantation window. The timing of first hCG detection was significantly later for the EPL group. Pregnancies that resulted in LB had consistently rising average daily IhCG and BhCG levels, with no significant differences when average daily IhCG and BhCG measurements were compared (Student t-test, P > 0.05), whereas pregnancies that resulted in CAB and EFL had lower average daily IhCG and BhCG levels that increased inconsistently. These findings demonstrate that critical information related to pregnancy outcome may be present when multiple urinary hCG isoforms are measured. Further data suggest that the rate of change for the ratio of daily BhCG over IhCG levels might be useful as the basis of a broadly applicable early biomarker for pregnancy outcome.