[1] Karolinska Inst, Dept Med Epidemiol & Biostat, SE-17177 Stockholm, Sweden
[2] Karolinska Univ Hosp, Astrid Lindgren Childrens Hosp, Dept Womens & Childrens Hlth, Stockholm, Sweden
[3] Stockholm S Gen Hosp, Sodersjukhuset, Dept Obstet & Gynaecol, Stockholm, Sweden