Funding for this research was provided by:
Science and Technology Fund of Tianjin Health and Family Planning Commission (15KG132)
Received: 4 November 2019
Accepted: 25 March 2020
First Online: 7 April 2020
Ethics approval and consent to participate
: This cross-sectional study was conducted at the Tianjin First Central Hospital from December 2014 to August 2016. The study was approved by the local ethics committee. Written informed consent was obtained from all participants.
: Not applicable.
: The authors declare that they have no competing interests.