[1
]
Department of Obstetrics and Gynecology, Shandong Provincial Hospital, Shandong University,
Jinan, People's Republic of China. Electronic address: lichangzhong@hotmail.com.
[2
]
Department of Oncology, Shandong Tumor Hospital, Jinan, People's Republic of China.
[3
]
Department of Obstetrics and Gynecology, Shandong Provincial Hospital, Shandong University,
Jinan, People's Republic of China.
[4
]
School of Public Health, Shandong University, Jinan, People's Republic of China.