作者单位:Childrens Hosp, Div Neonatal Med, Boston, MA 02115 USA[1]Primary Childrens Med Ctr, Salt Lake City, UT USA[2]Intermt Healthcare, Women & Newborns Clin Program, Salt Lake City, UT USA[3]LDS Hosp, Stat Data Ctr, Salt Lake City, UT USA[4]Univ Utah, Sch Med, Div Hematol Oncol, Dept Pediat, Salt Lake City, UT 84108 USA[5]