Received December 02, 2020
Accepted June 15, 2021

Objective: To study the predictive value of serum β-hCG on day 5 after frozen-thawed embryo transfer (FET) to predict pregnancy outcomes and to establish cut-off values for very early biochemical pregnancy diagnosis. Methods: This retrospective cohort study was performed at a private reproductive medicine centre and the medical records of women who underwent FET cycles from January 2018 to June 2019 were reviewed. A total of 116 evaluated cycles had serum β-hCG levels measured on days 5 and 10 after FET. The predictive value of serum β-hCG levels measured on day 5 after FET was investigated for very early biochemical pregnancy diagnosis. Results: The standard biochemical pregnancy diagnosis was defined as β-hCG ≥ 25 IU/mL. A receiver operating characteristic curve was generated, and the cut-off value of β-hCG on day 5 for predicting biochemical pregnancies was 4.0 IU/L, with 93.4% sensitivity and 92.7% specificity (AUC, 0.960; 95% confidence interval, 0.923–0.997). Conclusion: Values for β-hCG at day 5 after FET ≥ 4.0 IU/L are accurate for the diagnosis of biochemical pregnancy. The use of very early biochemical pregnancy diagnosis in clinical practise allows earlier management, counselling of patients, and appropriate follow-up.