[1] IRCCS Ca Granda Fdn, Maggiore Policlin Hosp, Via M Fanti 6, I-20122 Milan, Italy
[2] Univ Edinburgh, Chalmers Sexual & Reprod Hlth Serv, Edinburgh, Midlothian, Scotland
[3] Univ Edinburgh, Simpson Ctr Reprod Hlth, Edinburgh, Midlothian, Scotland
[4] British Pregnancy Advisory Serv, Doncaster, England
[5] Hop Kremlin Bicetre, CESP Gender Sexual & Reprod Hlth, Inserm U1018, Le Kremlin Bicetre, France
[6] Johns Hopkins Univ, Dept Populat Family & Reprod Hlth, Bloomberg Sch Publ Hlth, Baltimore, MD USA
[7] Aarhus Univ, Natl Ctr Register Based Res, Aarhus V, Denmark
[8] Innlandet Hosp Trust, Lillehammer, Norway
[9] Univ Aberdeen, Dept Obstet & Gynaecol, Maternal Hosp, Foresterhill, Aberdeen, Scotland
[10] Univ Edinburgh, Ctr Reprod Biol, Edinburgh, Midlothian, Scotland
[11] Univ Milan, Dept Clin Sci & Community Hlth, Milan, Italy
[12] IRCCS Ist Ric Farmacol Mario Negri, Dept Epidemiol, Milan, Italy
[13] Univ Modena, Dipartimento Integrato Materno Infantile, Modena, Italy