[1] Columbia Univ, Sch Nursing, New York, NY 10032 USA
[2] Univ Calif Los Angeles, David Geffen Sch Med, Los Angeles, CA USA
[3] Columbia Univ, Irving Med Ctr, Dept Obstet & Gynecol, Div Maternal Fetal Med, New York, NY USA
[4] Univ Calif Berkeley, Sch Publ Hlth, Berkeley, CA USA