Xu, X.
Wu, L.
Lu, Z. Q.
Xia, P.
Zhu, X. P.
Gao, X.
Funding for this research was provided by:
grants of the Shanghai Municipal Health Project grant (Grant No. 2013ZYJB0802)
Shanghai Health and Family Planning Commission Foundation (Grant No.12GWZX0103, 2013SY005)