Funding for this research was provided by:
Beijing Municipal Science & Technology Commission (Z181100001718091)
Text and Data Mining valid from 2019-08-13
Received: 7 January 2019
Accepted: 6 August 2019
First Online: 13 August 2019
Ethics approval and consent to participate
: The protocol for recruitment and collection of baseline data and biological samples for the cohort has been approved by the Medical Ethics Committee of Beijing Obstetrics and Gynecology Hospital, Capital Medical University. All participants in this research provided their written consent.
: Not applicable.
: The authors declare that they have no competing interests.