[1] Vanderbilt Univ, Dept Biomed Engn, VU Stn B Box 351631, Nashville, TN 37235 USA
[2] Meharry Med Coll, Dept Obstetr & Gynecol, Nashville, TN 37208 USA
[3] Vanderbilt Univ, Dept Neonatol, Nashville, TN 37232 USA
[4] Vanderbilt Univ, Dept Obstetr & Gynecol, Nashville, TN 37232 USA