Article History
Received: 3 April 2019
Accepted: 30 December 2019
First Online: 9 January 2020
Ethics approval and consent to participate
: The Ethics Committee of the Obstetrics and Gynecology Hospital, Fudan University approved this study on June 2018, under the registration number: 218–47. All patients signed an informed consent document before the study.
: Not applicable.
: The authors declare that they have no competing interests.