作者单位:Columbia Univ Coll Phys & Surg, New York, NY 10032 USA[1]Columbia Univ, Joseph L Mailman Sch Publ Hlth, Dept Biostat, New York, NY USA[2]Christiana Care Hlth Syst, Dept Obstet & Gynecol, Wilmington, DE USA[3]Columbia Univ, Dept Obstet & Gynecol, Div Maternal Fetal Med, Med Ctr, New York, NY 10032 USA[4]