1. Department of Obstetrics and Gynecology, Guangzhou Women and Children’s Medical Center, Guangzhou, China
2. Department of Obstetrics and Gynecology, Valleywise Health/District Medical Group, 2601 E. Roosevelt Road, Phoenix, AZ, USA
3. Department of Obstetrics and Gynecology, University of Arizona College of Medicine-Phoenix, Phoenix, AZ, USA
4. School of Public Health, Sun Yat-sen University, Guangzhou, China