Department of obstetrics Hainan General Hospital Hainan Affifliated Hospital of Hainan Medical University Haikou Hainan China 570311;
Department of obstetrics Hainan General Hospital Hainan Affifliated Hospital of Hainan Medical University Haikou Hainan China 570311;
Department of obstetrics Hainan General Hospital Hainan Affifliated Hospital of Hainan Medical University Haikou Hainan China 570311;