BeijingObstetricsandGynecologyHospital;
AffilitedHospitalofCapitalUniversityofMedicalSciences;
Beijing100006;
China;
ResearchInstituteforFamilyPlanningofHunan;
Changsha410005;
China;
Obstestrics&GynaecologyHospital;
FudanUniversitySchoolofMedicine;
Shanghai200011;
China;
ResearchInstituteforFamilyPlanningofLiaoning;
Shenyan110031;
China;
ResearchInstituteforFamilyPlanningofHebei;
Shijiazhuang050071;
China;
ResearchInstituteforFamilyPlanningofJiangsu;
Nanjing210036;
China;
ResearchInstituteforFamilyPlanningofGuizhou;
Guiyang550004;
China;
ResearchInstituteforFamilyPlanningofYunnan;
Kunming650021;
China;
ResearchInstituteforFamilyPlanningofHenan;
Zhengzhou450003;
China;