1. Department of Obstetrics and Gynecology, China-Japan Union Hospital, Jilin University, Changchun, Jilin, People’s Republic of China
2. Department of Histology & Embryology, School of Basic Medical Sciences, Jilin University, Changchun, Jilin, People’s Republic of China
3. Department of Histology & Embryology, Guangdong Medical University, Dongguan, Guangdong, People’s Republic of China