Dan Med J 2015; 62 (8): A5111

2 danish mEdical JOURnal Dan Med J 62/8 August 2015 or, in case of a non-adopted child, the time of adoption of the adoptee with whom the child was matched. An early two-year post-adoption period covers the first two full calendar years following the adoption year and represents the post-adoption recovery period. A late threeyear post-adoption period spans the three calendar years following the early post-adoption period. Healthcare utilisation is measured for selected primary care contacts or hospital admissions (see below), as the total number of these contacts in each of the post-adoption periods. Data on contacts to primary care up to 2005 were retrieved from the Danish National Health Services Register [12]. These data were registered under the childs own identification number only as from 1997. Therefore, analyses on primary care outcomes for the early post-adoption period included only those adopted in the 1996-2003 period, and for the late post-adoption period only those adopted in the 1994-2000 period; these periods do not end by 2005 to ensure that all children have two and three years of follow-up, respectively. Data on diagnoses for in-and outpatient contacts to secondary care were obtained from the Danish national patient register (NPR)[13] and used the same inclusion years as the primary care analyses. If, for a certain person, register data were only available for part of a period, the available outcome information (eg days in hospital, number) was divided by the fraction of the period for which information was available.