Funding for this research was provided by:
National Natural Science Foundation of China (81671482, 31401226)
Text and Data Mining valid from 2018-06-20
Received: 28 February 2018
Accepted: 15 June 2018
First Online: 20 June 2018
Ethics approval and consent to participate
: The study was approved by the Institutional Review Board of the International Peace Maternity and Child Health Hospital, Shanghai, China [GKLW 2016–42].
: Not applicable.
: The authors declare that they have no competing interests.
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