1. Department of Obstetrics and Gynecology, Family Planning Service Center of Yiwu Maternity and Child Health Care Hospital, Yiwu, Zhejiang 322000, P.R. China
2. Department of Galactophore, Family Planning Service Center of Yiwu Maternity and Child Health Care Hospital, Yiwu, Zhejiang 322000, P.R. China
3. Department of Human Health and Human Service, Family Planning Service Center of Yiwu Maternity and Child Health Care Hospital, Yiwu, Zhejiang 322000, P.R. China
4. Department of Public Health, Southwest Medical University, Luzhou, Sichuan 646600, P.R. China
5. Department of Obstetrics and Gynecology, The Third Hospital of Hebei Medical University, Shijiazhuang, Hebei 050035, P.R. China