Can biochemical pregnancy be determined 5 days after frozen-thawed embryo transfer?

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 we reviewed the medical records of women who underwent FET cycles from January 2018 to June 2019. 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 a β-hCG ≥25 IU/L on day 10 after FET. We then generated a receiver operating characteristic curve, 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). CONCLUSIONS: Values for β-hCG at day 5 after FET ≥4.0IU/L are accurate for the diagnosis of biochemical pregnancy. The use of very early biochemical pregnancy diagnosis in clinical practice enables earlier management, patient counselling, and appropriate follow-up.