[1] Royal Coll Gynaecologists & Obstetricians, Natl Collaborating Ctr Womens & Childrens Hlth, London NW1 4RG, England
[2] Univ Coll London Hosp, London E1 1BB, England
[3] Univ Glasgow, Reprod & Maternal Med, Glasgow, Lanark, Scotland
[4] Glasgow Royal Infirm, Glasgow G4 0SF, Lanark, Scotland