[1] UCL Inst Child Hlth, London, England
[2] Great Ormond St Hosp Sick Children, Great Ormond St, London WC1N 3JH, England
[3] Mt Sinai Hosp, Maternal Fetal Med Unit, Toronto, ON M5G 1X5, Canada
[4] Hosp Sick Children, Div Gen & Thorac Surg, 555 Univ Ave, Toronto, ON M5G 1X8, Canada
[5] Mt Sinai Hosp, Dept Pediat, Toronto, ON M5G 1X5, Canada
[6] Univ Lausanne Hosp, Dept Obstet & Gynecol, Maternofetal & Obstet Res Unit, Matern, Lausanne, Switzerland