Funding for this research was provided by:
Science and Technology Commission of Shanghai Municipality (PKJ 2014-S31)
Received: 14 December 2018
Accepted: 13 August 2019
First Online: 22 August 2019
Ethics approval and consent to participate
: The waiver was obtained from the Ethics Review Board of Jiading District Maternal and Children Health Hospital of Shanghai approving this research on residual specimens unlinked to personal identifiers.
: Not applicable.
: The authors declare that they have no competing interests.