[1] Dartmouth Inst Hlth Policy & Clin Practice, Geisel Sch Med, Lebanon, NH USA
[2] Geisel Sch Med, Dept Epidemiol, Lebanon, NH USA
[3] Georgia Gwinnett Coll, Sch Liberal Arts, Dept Human Serv & Cultural Studies, Lawrenceville, GA USA
[4] Dartmouth Hitchcock Med Ctr, OB GYN Dept, Lebanon, NH USA
[5] Dartmouth Inst Hlth Policy & Clin Practice, Geisel Sch Med, Dept Epidemiol, Williamson Translat Res Bldg, Rm 538, 1 Med Ctr Dr, Lebanon, NH 03756 USA