Funding for this research was provided by:
National Natural Science Foundation of China (81573231)
Shanghai Municipal Population and Family Planning Commission (15GWZK0801)
Received: 14 September 2018
Accepted: 11 April 2019
First Online: 29 April 2019
Ethics approval and consent to participate
: The study was approved by the Ethical Review Committee of the School of Public Health at Shanghai Jiao Tong University. All study participants signed a written informed consent form before enrollment.
: Not applicable.
: The authors declare that they have no competing interests.
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