[1] Univ Calif San Francisco, Sch Med, Dept Obstet Gynecol & Reprod Med, Div Maternal Fetal Med, San Francisco, CA 94143 USA
[2] Massachusetts Gen Hosp, Dept Obstet & Gynecol, Div Maternal Fetal Med, Boston, MA 02114 USA
[3] Oregon Hlth & Sci Univ, Dept Obstet & Gynecol, Portland, OR 97201 USA
[4] Univ Penn, Sch Med, Dept Family & Community Med, Philadelphia, PA 19104 USA