HebeiFamilyPlanningInstitute,Shi]iazhuang,China;
NationalResearchInstituteforfamilyPlanning,Bei/ing,China;
ShandongFamilyPlanningInatitute,Jinan,China;
ShanxiMaternityHospital,Xian,China;
TheSecondAffiliatedHospital,ZhongshanMedicalUniversity.Guangzhou.China;
XinHuaHospital,Shanghai,China;