[1] Univ Toronto, Fac Med, Inst Med Sci, Toronto, ON, Canada
[2] Mt Sinai Hosp, Dept Obstet & Gynaecol, Maternal Fetal Med, Toronto, ON, Canada
[3] Univ Toronto, Fac Med, MD Program, Toronto, ON, Canada
[4] Womens Coll Hosp, Womens Coll Res Inst, Toronto, ON, Canada
[5] Univ Toronto, Dalla Lana Sch Publ Hlth, Toronto, ON, Canada
[6] Univ Toronto, Dept Obstet & Gynaecol, Toronto, ON, Canada