Research question: Does the blastocyst development stage on embryo transfer day affect serum β-human chorionic gonadotrophin (β-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: β-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 β-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 β-HCG concentration between blastocysts of different development stages 9 and 16 days after transfer.
Conclusions: Faster-growing blastocysts produced significantly higher serum β-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, β-HCG concentrations 9 and 16 days after embryo transfer in FET cycles were higher than in fresh embryo transfer cycles. Interpretation of β-HCG results 9 days after blastocyst transfer should consider the blastocyst growth rate and whether fresh or cryopreserved embryo was transferred.
Keywords: Blastocyst development stage; Early pregnancy; IVF; Implantation; β-human chorionic gonadotrophin.
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