[1] Univ British Columbia, Dept Obstet & Gynecol, Vancouver, BC V6Z 2K8, Canada
[2] Univ British Columbia, Dept Family Practice, Vancouver, BC V6Z 2K8, Canada
[3] Univ British Columbia, Dept Family Med, Div Midwifery, Vancouver, BC V6Z 2K8, Canada
[4] Univ Alberta, Dept Obstet & Gynaecol, Edmonton, AB T6G 2R3, Canada
[5] Univ British Columbia, Fac Med, Womens Hlth Res Inst, Vancouver, BC V6Z 2K8, Canada