[1] Oslo Univ Hosp, Women & Childrens Div, N-0450 Oslo, Norway
[2] Univ Oslo, Oslo, Norway
[3] Univ British Columbia, Dept Obstet & Gynaecol, Vancouver, BC V5Z 1M9, Canada
[4] Univ British Columbia, Child & Family Res Inst, Vancouver, BC V5Z 1M9, Canada
[5] Univ Oxford, Oxford, England
[6] Univ Pittsburgh, Magee Womens Res Inst, Dept Epidemiol & Clin & Translat Res, Pittsburgh, PA USA
[7] Univ Pittsburgh, Magee Womens Res Inst, Dept Obstet Gynecol & Reprod Sci, Pittsburgh, PA USA
[8] Wake Forest Univ, Winston Salem, NC 27109 USA
[9] Univ Cambridge, Dept Obstet & Gynaecol, Cambridge, England
[10] Univ Cambridge, Ctr Trophoblast Res, Cambridge, England
[11] Cambridge Comprehens Biomed Res Ctr, Natl Inst Hlth Res, Cambridge, England