[1] UCL, Fac Populat Hlth Sci, EGA Inst Womens Hlth, London, England
[2] St George Hosp, Dept Obstet & Gynecol, Fetal Med Unit, London, England
[3] Univ Utah, Hlth Sci Ctr, Dept Radiol & Imaging Sci, Salt Lake City, UT USA
[4] Univ Louvain, St Luc Univ Hosp, Dept Obstet, Brussels, Belgium
[5] Univ Oxford, John Radcliffe Hosp, Nuffield Dept Obstet & Gynecol, Oxford, England
[6] John Radcliffe Hosp, Fetal Med Unit, Oxford, England