[1] Univ N Carolina, Sch Med, Div Maternal Fetal Med, Dept Obstet & Gynecol, 3010 Old Clin Bldg,CB 7516, Chapel Hill, NC 27599 USA
[2] Univ N Carolina, Sch Med, Chapel Hill, NC 27515 USA
[3] Univ N Carolina, Sch Med, Dept Social Med, Chapel Hill, NC 27515 USA
[4] Univ N Carolina, Sch Med, Ctr Bioeth, Chapel Hill, NC 27515 USA