Funding for this research was provided by:
This study was supported by the general medical research program of Zhejiang province in 2014 (2014KYA240)
Received: 30 May 2017
Accepted: 11 January 2018
First Online: 16 January 2018
Ethics approval and consent to participate
: This study was approved by the ethical review board of Zhejiang provincial center for disease control and prevention. Written informed consent was obtained from every pregnant woman once there was a decision to participate.
: Not applicable.
: The authors declare that they have no competing interests.
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