[1] Univ Toronto, Mt Sinai Hosp, Obstet & Gynaecol, Toronto, ON M5G 1X5, Canada
[2] Univ Toronto, Sunnybrook Hlth Sci Ctr, Dept Newborn & Dev Paediat, Toronto, ON, Canada
[3] Univ Toronto, SickKids Res Inst, Program Child Hlth Evaluat Sci, Toronto, ON, Canada
[4] Univ Toronto, Div Biostat, Toronto, ON, Canada
[5] Univ Toronto, Mt Sinai Hosp, Dept Paediat, Toronto, ON M5G 1X5, Canada
[6] McMaster Univ, Med Ctr, Dept Paediat, Hamilton, ON, Canada
[7] Univ Toronto, Dept Physiol, Toronto, ON, Canada
[8] Univ Toronto, Dept Obstet & Gynecol, Toronto, ON, Canada
[9] Univ Toronto, Dept Med, Toronto, ON, Canada
[10] Univ British Columbia, BC Womens Hosp, Dept Obstet & Gynaecol, Vancouver, BC V5Z 1M9, Canada
[11] Mackenzie Hlth, Dept Obstet & Gynaecol, Richmond Hill, ON, Canada
[12] McMaster Univ, Dept Clin Epidemiol & Biostat, Ctr Hlth Econ & Policy Anal, Hamilton, ON, Canada
[13] Dalhousie Univ, IWK Hlth Ctr, Dept Obstet & Gynaecol, Halifax, NS, Canada
[14] Univ Toronto, Sunnybrook Hlth Sci Ctr, Ctr Mother Infant & Child Res, Toronto, ON, Canada