[1] Burlo Garofolo Childrens Hosp, Epidemiol Unit, I-34137 Trieste, Italy
[2] Burlo Garofolo Childrens Hosp, Neonatal Intens Care Unit, I-34137 Trieste, Italy
[3] INSERM, U149, Epidemiol Unit Womens & Childrens Hlth, Villejuif, France
[4] Univ Halle Wittenberg, Dept Pediat, Halle, Germany
[5] Univ Amsterdam, Dept Neonatol, Amsterdam, Netherlands
[6] Fac Med Toulouse, INSERM, CJF 8908, Unit Res Reprod, F-31073 Toulouse, France
[7] Ctr Med Technol Assessment, Linkoping, Sweden
[8] Miguel Hernandez Univ, Dept Publ Hlth, Alicante, Spain
[9] Univ Glasgow, Dept Publ Hlth, Glasgow G12 8QQ, Lanark, Scotland
[10] Univ Dusseldorf, Dept Pediat, D-4000 Dusseldorf, Germany
[11] Bambino Gesu Childrens Hosp, Neonatal Intens Care Unit, Rome, Italy
[12] Natl Res Council, IFC, Div Epidemiol, Pisa, Italy