[1] Penn Hosp, Dept Obstet & Gynecol, Philadelphia, PA 19107 USA
[2] Massachusetts Gen Hosp, Dept Med, Boston, MA 02114 USA
[3] Thomas Jefferson Univ Hosp, Div Maternal Fetal Med, Dept Obstet & Gynecol, Philadelphia, PA 19107 USA
[4] Abington Mem Hosp, Dept Obstet & Gynecol, Div Maternal Fetal Med, Abington, PA 19001 USA