1 Department of Pediatrics, Tong Xiang Maternity and Child Health Care Hospital, Tongxiang, Zhejiang, China.
2 Department of Obstetrics and Gynecology, University of Alberta, Edmonton, AB, Canada.
3 Department of Pediatric Respiratory Medicine, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China. Electronic address: dingguodong@sjtu.edu.cn.