[1] Aberdeen Royal Infirm, Dept Gynaecol, Ward 315, Aberdeen, Scotland
[2] Univ Aberdeen, Div Appl Hlth Sci, Med Stat Team, Aberdeen, Scotland
[3] Aberdeen Matern Hosp, Dugald Baird Ctr, Aberdeen, Scotland
[4] Southampton Univ Hosp, Dept Obstet & Gynaecol, Southampton, Hants, England
[5] Univ Edinburgh, MRC Ctr Reprod Hlth, Edinburgh, Midlothian, Scotland
[6] Univ Aberdeen, Sch Med & Dent, Div Appl Hlth Sci, Aberdeen, Scotland