1. Reproductive Center, Yantaishan Hospital, Yantai, Shandong 264001, P.R. China
2. Department of Blood Transfusion, Yuhuangding Hospital, Yantai, Shandong 264000, P.R. China
3. Clinical Laboratory, People's Hospital of Rizhao, Rizhao, Shandong 276826, P.R. China
4. Department of Obstetrics, People's Hospital of Zhangqiu District, Jinan, Shandong 250200, P.R. China
5. Clinical Laboratory, Yuhuangding Hospital, Yantai, Shandong 264000, P.R. China