[1] Univ Helsinki, Dept Obstet & Gynaecol, Helsinki, Finland
[2] Helsinki Univ Hosp, Helsinki, Finland
[3] Finnish Inst Hlth & Welf, Helsinki, Finland
[4] Acad Primary Hlth Care Ctr Reg Stockholm, Stockholm, Sweden
[5] Karolinska Inst, Dept Mol Med & Surg, Stockholm, Sweden
[6] Univ Helsinki, New Childrens Hosp, Dept Orthopaed & Traumatol, Helsinki, Finland