[1] Aarhus Univ, Dept Clin Med, Palle Juul Jensens Blvd 99, DK-8200 Aarhus N, Denmark
[2] Aarhus Univ Hosp, Dept Obstet & Gynaecol, Skejby, Denmark
[3] Aarhus Univ Hosp, Ctr Res Rehabil CORIR, Aarhus, Denmark
[4] Aarhus Univ Hosp, Dept Clin Epidemiol, Aarhus, Denmark
[5] Univ Calif Los Angeles, Sch Publ Hlth, Epidemiol Sect, Los Angeles, CA 90024 USA