NationalResearchInstituteforFamilyPlanning;
Beijing100081;
China;
QingdaoResearchInstituteforFamilyPlanning;
Shangdong266076;
China;
TianjinResearchInstituteforFamilyPlanning;
Tianjin300000;
China;
ChaoyangHospital;
Beijing100081;
China;
TongjiMedicalUniversityResearchInstituteforFamilyPlanning;
Wuhan430000;
China;
BeijingShuangjingHospital;
Beijing100000;
China;
ScienceDepartmentofStateFamilyPlanningCommission;
Beijing100088;
China;