Predicting Ectopic Pregnancy Using Human Chorionic Gonadotropin (hCG) Levels and Main Cause of Infertility in Women Undergoing Assisted Reproductive Treatment: Retrospective Observational Cohort Study - Xu, Huiyu; Feng, Guoshuang; Wei, Yuan; Feng, Ying; Yang, Rui; Wang, Liying; Zhang, Hongxia; Li, Rong; Qiao, Jie (JMIR Medical Informatics, 2020)