1. Department of Reproductive Medicine, Yantaishan Hospital, Yantai, Shandong 264001, P.R. China
2. Department of Obstetrics, People's Hospital of Zhangqiu, Jinan, Shandong 250200, P.R. China
3. Department of Nursing, People's Hospital of Zhangqiu, Jinan, Shandong 250200, P.R. China
4. Department of Mingzhu Community Service Station, People's Hospital of Zhangqiu, Jinan, Shandong 250200, P.R. China
5. Department of Clinical Laboratory, Yantai Yuhuangding Hospital, Yantai, Shandong 264000, P.R. China