[1] Univ Oslo, Ulleval Hosp, Dept Obstet & Gynaecol, N-0424 Oslo, Norway
[2] Univ Oslo, Ulleval Hosp, Dept Haematol, N-0424 Oslo, Norway
[3] Univ Oslo, Inst Clin Med, N-0424 Oslo, Norway
[4] Univ Tromso, Dept Obstet & Gynaecol, Dept Clin Med, Tromso, Norway