Association between 7-day serum β-hCG levels after frozen–thawed embryo transfer and pregnancy outcomes: a single-centre retrospective study from China

OBJECTIVE: Early monitoring of plasma human chorionic gonadotropin (β-hCG) level is vital in predicting pregnancy outcome. This study investigated the predictive value of serum β-hCG level on the seventh day after frozen–thawed embryo transfer (FET) for ongoing pregnancy (OP) and adverse pregnancy (AP). DESIGN: Retrospective study. SETTING: The Reproductive and Genetic Center of the Affiliated Hospital of Shandong University of Traditional Chinese Medicine, China. PARTICIPANTS: 1061 pregnant women who underwent FET between January 2014 and January 2017. PRIMARY AND SECONDARY OUTCOME MEASURES: Pregnancy outcome. RESULTS: Serum β-hCG levels on the seventh day after FET were higher in the single OP group compared with the biochemical pregnancy group (p<0.001). Besides, the serum β-hCG cut-off level at 4.34 mIU/mL on the seventh day showed high predictive value (area under the curve (AUC)=0.852). Serum β-hCG levels on the seventh day after FET were higher in the twin OP group compared with the single OP group (p<0.001). Also, the serum β-hCG cut-off level at 17.95 mIU/mL on the seventh day showed high predictive value (AUC=0.903). Serum β-hCG levels on the seventh day after FET were lower in the ectopic pregnancy group compared with the single OP group (p<0.001) whereas, serum β-hCG cut-off level at 4.53 mIU/mL on the seventh day exhibited a high predictive value (AUC=0.860). Further, the serum β-hCG levels on the seventh day after FET were lower in the single early spontaneous abortion group compared with the single OP group (p<0.001) while the serum β-hCG cut-off level at 5.34 mIU/mL on the seventh day exhibited high predictive value (AUC=0.738). CONCLUSION: Serum β-hCG on the seventh day after FET has good clinical significance for the prediction of OP and AP.