Department;
of;
Obstetrics;
and;
Gynecology,;
First;
Affiliated;
Hospital,;
Medical;
College,;
Xi'an;
Jiaotong;
University,;
Xi;
'an;
710061,;
China;
Department;
of;
Obstetrics;
and;
Gynecology,;
Nanhai;
People's;
Hospital,;
Foshan;
528000,;
China;
Department;
of;
Mathematics;
and;
Statistics,;
University;
of;
Maryland;
Baltimore;
County,;
Baltimore,;
MD;
21250,;
USA;