Evaluation of a New Model for Human Chorionic Gonadotropin Rise in Pregnancies of Unknown Viability

OBJECTIVE:To evaluate the performance of a new human chorionic gonadotropin (hCG) threshold model to classify pregnancies as viable or nonviable using a longitudinal cohort of individuals with pregnancy of unknown viability. The secondary objective was to compare the new model with three established models.METHODS:This is a single-center, retrospective cohort study of individuals seen at the University of Missouri from January 1, 2015, until March 1, 2020, who had at least two consecutive quantitative hCG serum levels with an initial level greater than 2 milli-international units/mL and 5,000 milli-international units/mL or less, with the first interval between laboratory draws no greater than 7 days. Prevalence of correct classification of viable intrauterine pregnancies, ectopic pregnancies, and early pregnancy losses was evaluated with a new proposed hCG threshold model and compared with three established models describing minimum expected rates of hCG rise for a viable intrauterine pregnancy.RESULTS:Of an initial cohort of 1,295 individuals, 688 patients met inclusion criteria. One hundred sixty-seven individuals (24.3%) had a viable intrauterine pregnancy; 463 (67.3%) had an early pregnancy loss; and 58 (8.4%) had an ectopic pregnancy. A new model based on the total additive percent rise of hCG at 4 and 6 days after initial hCG (70% or greater and 200% or greater rise, respectively) was created. The new model was able to correctly identify 100% of viable intrauterine pregnancies while minimizing incorrect classification of early pregnancy losses and ectopic pregnancies as normal pregnancies. At 4 days after initial hCG, 14 ectopic pregnancies (24.1%) and 44 early pregnancy losses (9.5%) were incorrectly classified as potentially normal pregnancies. At 6 days after initial hCG, only seven ectopic pregnancies (12.1%) and 25 early pregnancy losses (5.6%) were incorrectly classified as potentially normal pregnancies. In established models, up to nine intrauterine pregnancies (5.4%) were misclassified as abnormal pregnancies and up to 26 ectopic pregnancies (44.8%) and 58 early pregnancy losses (12.5%) were incorrectly classified as potentially normal pregnancies.CONCLUSION:The proposed new hCG threshold model optimizes a balance between identifying potentially viable intrauterine pregnancies and minimizing misdiagnosis of ectopic pregnancies and early pregnancy losses. External validation in other cohorts is needed before widespread clinical use.