1. Perinatal Epidemiology Research Unit; Department of Paediatrics; Aarhus University Hospital; Aarhus Denmark
2. Department of Public Health; Section for Epidemiology; Aarhus University; Aarhus Denmark
3. The Fertility Clinic; Department of Obstetrics and Gynaecology; Herlev University Hospital; Herlev Denmark
4. Department of Obstetrics and Gynaecology; Aarhus University Hospital; Aarhus Denmark