Funding for this research was provided by:
National Natural Science Foundation of China (81671482)
Shanghai Jiao Tong University (YG2016ZD07, YG2017QN39)
Received: 9 January 2018
Accepted: 24 April 2018
First Online: 12 May 2018
Ethics approval and consent to participate
: The study protocol was approved by the Institutional Review Board of the International Peace Maternity and Child Health Hospital, Shanghai, China. The approval number is GKLW 2016-42.
: The authors declare that they have no competing interests.
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