1. National Centre for Healthcare Research and Pharmacoepidemiology, Department of Statistics and Quantitative Methods, University of Milano-Bicocca, Milan, Italy
2. Department of Statistics and Quantitative Methods, Division of Biostatistics, Epidemiology and Public Health, Laboratory of Healthcare Research and Pharmacoepidemiology, University of Milano-Bicocca, Milan, Italy
3. Department of Medicine and Surgery, University of Milano-Bicocca, Milano, Italy
4. Department of Obstetrics and Gynecology, Ospedale San Gerardo, Monza, Italy