[1] Univ Calif San Diego, Div Reprod Endocrinol & Infertil, La Jolla, CA 92093 USA
[2] Univ Penn, Perlman Sch Med, Ctr Clin Epidemiol & Biostat, Philadelphia, PA 19104 USA
[3] Univ Penn, Perlman Sch Med, Dept Biostat & Epidemiol, Philadelphia, PA 19104 USA
[4] Univ So Calif, Keck Sch Med, Dept Obstet & Gynecol, Los Angeles, CA 90033 USA
[5] Univ So Calif, Keck Sch Med, Dept Prevent Med, Los Angeles, CA 90033 USA