[1] Univ Calif San Francisco, Dept Family & Community Med, San Francisco, CA 94143 USA
[2] Univ Calif San Francisco, Dept Obstet Gynecol & Reprod Sci, San Francisco, CA 94143 USA
[3] Univ Calif San Francisco, Ctr Reprod Hlth Res, San Francisco, CA 94143 USA
[4] Univ So Calif, Keck Sch Med, Dept Prevent Med, Inst Prevent Res, Los Angeles, CA 90033 USA
[5] Scripps Coll, Dept Biol, Claremont, CA 91711 USA
[6] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA 94143 USA