1 Key Laboratory of Birth Regulation and Control Technology of National Health Commission of China, Shandong Maternal and Child Health Care Hospital, Jinan, China.
2 School of Public Health, Zhengzhou University, Zhengzhou, China.
3 College of Jitang, North China University of Science and Technology, Tangshan, China.
4 School of Public Health, Xinxiang Medical University, Xinxiang, China.
5 School of Public Health and Management, Weifang Medical University, Weifang, China.