1. Reproductive Center, The 940th Hospital of Joint Logistics Support Force of Chinese People's Liberation Army, Lanzhou, Gansu 730050, P.R. China
2. Reproductive Center, The First Hospital of Shanxi Medical University, Taiyuan, Shanxi 030001, P.R. China
3. Reproductive Medicine Center, Hainan Maternal and Children's Medical Center, Haikou, Hainan 570206, P.R. China
4. Reproductive Medicine Center, The First Affiliated Hospital of Hainan Medical University, Haikou, Hainan 570102, P.R. China