[1] Univ Texas Med Branch, Dept Obstet & Gynecol, Div Basic Sci & Translat Res, MRB 11-158A,301 Univ Blvd, Galveston, TX 77555 USA
[2] Univ Pittsburgh, Grad Sch Publ Hlth, Dept Epidemiol, Pittsburgh, PA 15260 USA
[3] Texas A&M Univ, Dept Epidemiol & Biostat, Sch Publ Hlth, College Stn, TX USA
[4] Univ Texas Med Branch, Ctr Interdisciplinary Res Womens Hlth, Dept Obstet & Gynecol, Galveston, TX USA
[5] Univ Texas Med Branch, Dept Prevent Med & Populat Hlth, Galveston, TX 77555 USA