[1] Ottawa Gen Hosp, Dept Obstet & Gynecol, OMNI Res Grp, Clin Epidemiol Unit,Ottawa Hlth Res Inst, Ottawa, ON K1H 8L6, Canada
[2] Univ Ottawa, Dept Obstet & Gynecol, Div Maternal & Fetal Med, Ottawa, ON, Canada
[3] Ontario Perinatal Surveillance Syst, Ottawa, ON, Canada
[4] Queens Univ, Sch Med, Kingston, ON, Canada