[1] Yangzhou Univ, Sch Nursing, Yangzhou, Jiangsu, Peoples R China
[2] Sun Yat Sen Univ, Affiliated Hosp 8, Dept Obstet, Shenzhen, Guangdong, Peoples R China
[3] Yangzhou Univ, Med Coll, Dept Obstet & Gynecol, Yangzhou, Jiangsu, Peoples R China
[4] Yangzhou Univ, Med Coll, Yangzhou, Jiangsu, Peoples R China
[5] Ningbo Ctr Dis Control & Prevent, Ningbo, Peoples R China