[1] Univ Toronto, Ctr Res Womens Hlth, Maternal Infant & Reprod Hlth Res Unit, Toronto, ON M5G 1N8, Canada
[2] Sunnybrook & Womens Coll Hlth Sci Ctr, Dept Obstet & Gynaecol, Toronto, ON, Canada
[3] Univ Toronto, Ctr Res Womens Hlth, Fac Nursing, Toronto, ON M5G 1N8, Canada
[4] Univ Toronto, Ctr Res Womens Hlth, WHO Collaborating Ctr, Toronto, ON M5G 1N8, Canada
[5] Univ Toronto, Hosp Sick Children, Dept Paediat, Toronto, ON M5G 1N8, Canada
[6] Centenary Hosp, Dept Obstet & Gynaecol, Scarborough, ON, Canada
[7] Univ Manitoba, St Boniface Hosp, Dept Obstet & Gynaecol, Winnipeg, MB, Canada
[8] McMaster Univ, Dept Clin Epidemiol & Biostat, Hamilton, ON, Canada
[9] McMaster Univ, Dept Paediat, Hamilton, ON, Canada