[1] Raigmore Hosp, Dept Biochem, Inverness IV2 3UJ, Scotland
[2] Univ Edinburgh, Div Reprod & Dev Sci, Edinburgh, Midlothian, Scotland
[3] Royal Infirm Edinburgh NHS Trust, Edinburgh Fertil & Reprod Endocrine Ctr, Edinburgh, Midlothian, Scotland
[4] Glasgow Royal Infirm, Dept Clin Biochem, Glasgow G4 0SF, Lanark, Scotland