[1] Gartnavel Royal Hosp, Dept Intervent Radiol, Glasgow G12 0YN, Lanark, Scotland
[2] Vital Stat, Glasgow G11 7EE, Lanark, Scotland
[3] Univ Edinburgh, Dept Med Stat, Ctr Populat Hlth Sci, Edinburgh, Midlothian, Scotland
[4] Stobhill Gen Hosp, Glasgow G21 3UW, Lanark, Scotland
[5] Royal Infirm, Dept Med Educ & Gynaecol Reprod & Maternal Med, Glasgow G4 0SF, Lanark, Scotland