[1] Univ Colorado, Dept Obstet & Gynecol, Anschutz Med Campus, Aurora, CO USA
[2] Univ Michigan Hlth, Dept Obstet & Gynecol, Ann Arbor, MI USA
[3] ANEX Anesthesia, Dept Anesthesiol, Brookfield, WI USA
[4] Vanderbilt Univ, Med Ctr, Dept Anesthesia, Nashville, TN USA
[5] Vanderbilt Univ, Med Ctr, Dept Obstet & Gynecol, Nashville, TN USA
[6] Univ Colorado, Dept Obstet & Gynecol, Anschutz Med Campus,12631 E 17th Ave,Mail Stop B-1, Aurora, CO 80045 USA