Maternal β-HCG concentrations in early IVF pregnancy: association with the embryo development stage of blastocysts

Research question: Does the blastocyst development stage on embryo transfer day affect serum beta-human chorionic gonadotrophin (beta-HCG) concentration 9 and 16 days after embryo transfer in women whose pregnancy progresses beyond 13 weeks? Design: Retrospective study involving 204 cases where pregnancy progressed beyond 13 weeks of single blastocyst transfer in fresh (n = 66) or frozen embryo transfer (FET) (n = 138) cycles from January 2015 to September 2016. Results: beta-HCG concentrations 9 and 16 days after embryo transfer in FET cycles (median 223 IU/l and 4378 IU/l, respectively) were significantly (P < 0.001) higher than in fresh cycles (157 IU/l and 2813 IU/l). Among fresh cycles, faster-growing blastocysts (expanded + hatching + hatched blastocysts) produced significantly (P < 0.001) higher beta-HCG concentrations 9 days after embryo transfer (191 IU/l) than slower-growing blastocysts (cavitating + full blastocyst, 106 IU/l); however no significant difference was found between the faster- and slower-growing groups by day 16 (2359 IU/l and 3025 IU/l, respectively). Among FET cycles, there was no difference in beta-HCG concentration between blastocysts of different development stages 9 and 16 days after transfer. Conclusions: Faster-growing blastocysts produced significantly higher serum beta-HCG concentrations 9 days after transfer than slower-growing blastocysts in fresh cycles, but the difference was not significant by day 16 after transfer. Also, beta-HCG concentrations 9 and 16 days after embryo transfer in FET cycles were higher than in fresh embryo transfer cycles. Interpretation of beta-HCG results 9 days after blastocyst transfer should consider the blastocyst growth rate and whether fresh or cryopreserved embryo was transferred.