1. Department of Public Health, Section for EpidemiologyAarhus University Aarhus Denmark
2. Department of EpidemiologyFielding School of Public HealthUniversity of California Los Angeles California USA
3. Department of Public Health, Section for BiostatisticsAarhus University Aarhus Denmark
4. Department of Clinical EpidemiologyAarhus University Hospital Aarhus Denmark
5. Perinatal Epidemiology Research UnitDepartment of PaediatricsAarhus University Hospital Aarhus Denmark