Text and Data Mining valid from 2019-08-17
Received: 5 April 2019
Accepted: 18 July 2019
First Online: 17 August 2019
Ethics approval and consent to participate
: This research was approved by the Institutional Review Board of Center for Reproductive Medicine of Shandong University.
: Formal written consent was obtained from each patient.
: The authors declare that they have no competing interests.