[1] Univ Bristol, Sch Social & Community Med, Bristol BS8 2PS, Avon, England
[2] Univ Bristol, MRC Ctr Causal Anal Translat Epidemiol CAiTE, Bristol BS8 2PS, Avon, England
[3] McGill Univ, Fac Med, Dept Pediat, Montreal, PQ, Canada
[4] McGill Univ, Fac Med, Dept Epidemiol Biostat & Occupat Hlth, Montreal, PQ, Canada
[5] Natl Res & Appl Med Mother & Child Ctr, Minsk, BELARUS