Birthweight and work participation in adulthood

Background In a number of studies, birthweight has been associated with cognition and educational attainment into adult age. However, the association is not clear between birthweight and work participation in adulthood. We investigated this association assessing to which extent it was influenced by circumstances concerning family background or disease in early life. Methods Through linkage between several national registers containing personal information from birth into adult age we established a longitudinal, population-based cohort study. Study participants were all 308 829 singletons born in Norway in 1967–1971 as registered by the Medical Birth Registry of Norway who were national residents at age 29. The study outcome was unemployment defined as a lack of personal income among people who were not under education in the calendar year of their 29th birthday as registered by the National Insurance Administration and Statistics Norway. Results Birthweight below the standardized mean was associated with unemployment. The risk of unemployment increased by decreasing birthweight for both women and men and also after adjustment for potential confounding factors. The association was evident both in people with or without social disadvantage, as well as people with or without childhood disease. Still, birthweight below the standardized mean explained much less of the unemployment risk than did social disadvantage (attributable fractions 8.0 % versus 28.3 % for women and 10.0% versus 40.2 % for men). Conclusion Birthweight below the standardized mean was independently associated with unemployment at age 29, also in the normal birthweight range