[1] Oxford Univ Hosp NHS Fdn Trust, John Radcliffe Hosp, Womens Ctr, Oxford Fetal Med Unit, Oxford, England
[2] Frimley Hlth NHS Fdn Trust, Dept Obstet & Gynaecol, Wexham Pk Hosp, Slough, Berks, England
[3] Royal Berkshire NHS Fdn Trust, Dept Obstet & Gynaecol, Reading, Berks, England
[4] Milton Keynes Univ NHS Fdn Trust, Dept Obstet & Gynaecol, Milton Keynes, Bucks, England
[5] Cairo Univ, Fac Med, Dept Obstet & Gynecol, Cairo, Egypt
[6] Great Western Hosp NHS Fdn Trust, Dept Obstet & Gynaecol, Swindon, Wilts, England
[7] Oxford Acad Hlth Sci Network, Oxford, England