Affiliation: | 1 London School of Hygiene and Tropical Medicine, London WC1E 7HT;2 North Thames (West) Congenital Malformations Register, Northwick Park Hospital, Harrow, Middlesex HA1 3UJ;3 EUROCAT Central Registry, University of Ulster, Newtownabbey, Co Antrim, Northern Ireland BT37 OQB |