Funding for this research was provided by:
the Citic-Xiangya Research Fund (KYXM-201703)
the science and technology major project of the ministry of science and technology of Hunan Province, China (2017SK1030)
the China Postdoctoral Science Foundation funded project (2019M652778)
the science and technology project of Health and Family Planning Commission of Hunan Province, China (C20180289)
Received: 23 July 2019
Accepted: 17 February 2020
First Online: 17 March 2020
Ethics approval and consent to participate
: This study was approved by the Ethics Committee of the Reproductive and Genetic Hospital of CITIC-Xiangya (LL-SC-2019-013). The ethics committee waived the need for informed consent due to the retrospective study design. An administrative permission was acquired by our team to access the data used in this study.
: Not applicable.
: The authors declare that they have no competing interests.