[1] Univ Aberdeen, Dept Obstet & Gynaecol, Dugald Baird Ctr Res Womens Hlth, Aberdeen AB25 2ZL, Scotland
[2] Univ Aberdeen, Ctr Adv Studies Nursing, Aberdeen, Scotland
[3] Univ Sheffield, ScHARR, Med Care Res Unit, Sheffield S10 2TN, S Yorkshire, England
[4] Univ Edinburgh, Scottish Programme Clin Effectiveness Reprod Hlth, Edinburgh EH8 9YL, Midlothian, Scotland
[5] Univ Aberdeen, Scottish Programme Clin Effectiveness Reprod Hlth, Aberdeen AB9 1FX, Scotland