1. Department of Quality of Care and Health Economics, National Institute for Public Health and the Environment (RIVM), Centre for Nutrition, Prevention and Health Services , Bilthoven, the Netherlands
2. Department of Public Health and Primary Care/Health Campus The Hague, Leiden University Medical Centre , the Hague, the Netherlands
3. Department of Obstetrics and Gynaecology, Erasmus MC, University Medical Centre , Rotterdam, the Netherlands
4. National Perinatal Epidemiology Unit, Nuffield Department of Population Health, University of Oxford , Oxford, UK