1. Department of Nursing, Tianjin Medical College, Tianjin, China.
2. Department of Intensive Obstetrics/Obstetrics and Chengdu Women's and Children's Central Hospital, School of Medicine, University of Electronic Science and Technology of China, Chengdu, China.
3. Department of Nursing, Chengdu Women's and Children's Central Hospital, School of Medicine, University of Electronic Science and Technology of China, Chengdu, China.
4. Department of Obstetrics, Shenzhen People's Hospital, Shenzhen, China.