[1] Hlth Canada, Lab Ctr Dis Control, Bur Reprod & Child Hlth, Ottawa, ON K1A 0L2, Canada
[2] Univ Laval, Epidemiol Res Grp, St Foy, PQ G1K 7P4, Canada
[3] McGill Univ, Dept Pediat, Montreal, PQ H3A 2T5, Canada
[4] McGill Univ, Dept Epidemiol & Biostat, Montreal, PQ H3A 2T5, Canada
[5] Univ Med & Dent New Jersey, Robert Wood Johnson Med Sch, Dept Environm & Community Med, Piscataway, NJ 08854 USA