[1] Univ N Carolina, Sch Nursing, Carrington Hall,CB 7460, Chapel Hill, NC 27599 USA
[2] Thomas Jefferson Univ, Dept Obstet & Gynecol, Sidney Kimmel Med Coll, Philadelphia, PA 19107 USA
[3] Univ N Carolina, Sch Med, Dept Social Med, Chapel Hill, NC 27599 USA
[4] Univ N Carolina, Sch Med, Ctr Bioeth, Chapel Hill, NC 27599 USA
[5] Univ N Carolina, Sch Med, Dept Obstet & Gynecol, Chapel Hill, NC 27599 USA