Funding for this research was provided by:
National Natural Science Foundation of China (81170618)
Peking University Third Hospital (BYSY2015002)
Text and Data Mining valid from 2019-02-12
Received: 12 November 2018
Accepted: 31 January 2019
First Online: 12 February 2019
Ethics approval and consent to participate
: This study was approved by the Institutional Review Board at Reproductive Medicine Center of Peking University Third Hospital. All the participants provided written consent to participate in the study.
: Not applicable.
: The authors declare that they have no competing interests.
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