1. Shanghai First Maternity and Infant Hospital, Tongji University School of Medicine, Shanghai, People's Republic of China
2. Department of Obstetrics, International Peace Maternity & Child Health Hospital, Shanghai Jiaotong University Medical School, Shanghai, People's Republic of China
3. Division of Maternal Fetal Medicine, Department of Obstetrics & Gynecology, The Ohio State University College of Medicine, Columbus, Ohio