[1] Sun Yat Sen Univ, Affiliated Hosp 1, Fetal Med Ctr, Dept Obstet & Gynecol, Guangzhou 510275, Guangdong, Peoples R China
[2] Mercer Univ, Sch Med, Dept Biol Sci, Savannah, GA USA
[3] Mayo Clin, Dept Obstet & Gynecol, Rochester, MN USA
[4] Mayo Coll Med, Rochester, MN USA
[5] Mem Hlth Univ, Med Ctr, Dept Obstet & Gynecol, Savannah, GA USA
[6] Mayo Clin, Dept Med, Rochester, MN USA