Live Births After Low Initial β-hCG in IVF Cycles: A Retrospective Cohort Study

Background Serum beta-human chorionic gonadotropin (β-hCG) hormone is a well-established biomarker used for pregnancy monitoring and prognosis in in vitro fertilization (IVF) cycles. After embryo transfer, a high serum β-hCG level with a prompt doubling time is typically reassuring, while a low initial β-hCG often leads to counselling around likely impending pregnancy loss and/or ectopic pregnancy. However, the number of patients with low β-hCG who ultimately deliver a live birth is unclear. Methods This is a single-centre retrospective cohort study of IVF pregnancies between January 2019 and December 2022. Serum β-hCG was drawn 14 days post-fertilization. We considered an initial β-hCG ≤ 50 mIU/mL as low. A logistic mixed-effects regression model assessed the odds of live birth for every 10 mIU/mL increase in β-hCG, adjusting for patient and cycle characteristics (age, body mass index, embryo stage, number of embryos transferred, and preimplantation genetic testing for aneuploidy). Receiver operating characteristic curves were plotted to determine optimal cut-points. Results Among 2443 pregnancies, the prevalence of live birth was 12% for those with an initial β-hCG ≤ 50 mIU/mL. For each 10 mIU/mL difference in initial β-hCG, the odds of live birth increased significantly (aOR = 1.035, 95% CI: 1.027, 1.042). Receiver operating characteristic curve analysis showed that an initial β-hCG greater than 22.5 mIU/mL identified over 99% of patients who ultimately had a live birth (sensitivity 1, specificity 0.21, AUC 0.726). The rate of change from initial β-hCG demonstrated stronger discriminatory performance for live birth among patients with low initial β-hCG (AUC 0.876 [0.84, 0.91]) than among those with an initial β-hCG > 50 mIU/mL (AUC 0.584 [0.56, 0.61]). Conclusions While IVF pregnancies with a low initial β-hCG can result in live birth, the likelihood is low. The rate of β-hCG rise emerged as a stronger discriminator of pregnancy outcomes when the initial β-hCG is low. Live birth was extremely rare when the initial β-hCG was below 22.5 mIU/mL. These findings offer prognostic data to guide counselling and refine expectations after IVF.