This work was supported by grants from the National Natural Science Foundation of China (Nos. 81771656 and 81370763), Special fund for clinical research of the Chinese Medical Association (No. 16020480664), and the Merck Serono China Research Fund for Fertility Agreement. The authors have no competing interests.

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This work was supported by grants from the National Natural Science Foundation of China, Grant numbers 81771656 and 81370763; Clinical research special fund of Chinese Medical Association, Grant number 16020480664; Shanghai Jiao Tong University Medicine-Engineering Fund, Grant number YG2017ZD11 and YG2017MS57; and the Merck-Serono China Research Fund for Fertility Agreement. P.C.K.L. is supported by a Canadian Institutes of Health Research Foundation Scheme Grant 143317. None of the authors has any competing interests.