The association between serum β-hCG on day 24 of pregnancy and ongoing pregnancy in frozen embryo transfer cycles.

OBJECTIVE: To determine the relationship between serum levels of the β-subunit of human chorionic gonadotropin (β-hCG) on day 24 of pregnancy during a frozen embryo transfer (FET) cycle and ongoing pregnancy.

METHODS: In a retrospective cohort study, data were reviewed from women aged 38years or younger who underwent a FET cycle at Nanfang Hospital, Guangzhou, China, from January 2013 to December 2014. Inclusion criteria were use of hormone-replacement therapy to achieve an endometrial thickness of 8mm or more, and at least two surviving embryos. Serum β-hCG on day 24 of pregnancy was assessed in relation to ongoing pregnancy at 12weeks.

RESULTS: Overall, 217 patients who underwent 248 FET cycles were included. The only measure that differed between cycles with (n=112) and without (n=136) ongoing pregnancy was β-hCG level on day 24 of pregnancy (73.0±65.8 vs 19.4±34.5mIU/mL; P<0.001). Classification tree analysis showed that women with day-24 β-hCG levels higher than 26.6mIU/mL had a 75.8% likelihood of ongoing pregnancy. In receiver operating characteristic curve analysis, the corresponding area under curve was 0.845 (95% confidence interval 0.795-0.895).

CONCLUSION: A maternal serum β-hCG level higher than 26.6mIU/mL was predictive of ongoing pregnancy at 12weeks.