1 Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy.
2 Department of Obstetrics, Gynecology and Neonatology, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.
3 Unit of Biostatistics, Epidemiology and Public Health, Department of Statistics and Quantitative Methods, University of Milano-Bicocca, Milan, Italy.
4 National Center for Healthcare Research and Pharmacoepidemiology, Milan, Italy.