1. Medical Research Council Group in Fetal and Neonatal Health and Development (B.D., C.C., T.C., D.J.H.), Lawson Health Research Institute, London, Ontario, Canada N6A4V2
2. U257 Institut National de la Santé et de la Recherche Médicale (D.B., J.J., R.L.J.), 75014 Paris, France
3. Departments of Physiology, Medicine, and Paediatrics (D.J.H.), University of Western Ontario, London, Ontario, Canada N6A 5A5