[1] Cedars Sinai Med Ctr, Dept Obstet & Gynecol, Los Angeles, CA 90048 USA
[2] Oregon Hlth & Sci Univ, Portland, OR USA
[3] Univ Calif San Francisco, Dept Obstet Gynecol & Reprod Sci, San Francisco, CA 94143 USA
[4] Univ Calif San Francisco, Sch Nursing, Dept Family Hlth, San Francisco, CA 94143 USA