[1] Univ Western Ontario, Dept Anesthesiol & Perioperat Med, London, ON N6A 4V2, Canada
[2] Univ Western Ontario, Div Maternal Fetal Med, Dept Obstet & Gynaecol, London, ON N6A 4V2, Canada
[3] Univ Western Ontario, Dept Cardiol, London, ON N6A 4V2, Canada