Funding for this research was provided by:
Ministry of Science and Technology of the People's Republic of China (2016YFC10002)
Shandong Science and Technology Department (2017G006036, 2018YFJH0504)
Text and Data Mining valid from 2020-01-30
Received: 12 November 2019
Accepted: 20 January 2020
First Online: 30 January 2020
Ethics approval and consent to participate
: The present study was approved by the Local Medical Institutional Review Board of the Reproductive Medicine of Shandong University. Written informed consent was obtained from each participant.
: Not applicable.
: The authors declare that they have no competing interests.