Cumulative incidences of hospital-treated psychiatric disorders are increasing in five Finnish birth cohorts

Objective The aim of this study was to explore changes in the incidences of childhood and early adulthood hospital-treated psychiatric disorders in five large Finnish birth cohorts of individuals born between 1966 and 1997. Methods The five birth cohorts were as follows: Northern Finland Birth Cohort 1966 (NFBC 1966) and 1986 (NFBC 1986), 1987 Finnish Birth Cohort (FBC 1987) and 1997 (FBC 1997), and Finnish 1981 Birth Cohort Study (FBCS 1981). Incidences of hospital-treated psychiatric disorders in each cohort were calculated separately for males (N = 71,209) and females (N = 65,190). Poisson regression was used to test difference in proportions of psychiatric disorders in wide range of diagnosis classes separately in childhood and adolescence, and early adulthood. Results The total incidences of psychiatric disorders in childhood and adolescence among males has increased in the birth cohorts over decades (Incidence Rate Ratio, IRR = 1.04 (1.04-1.05); p < 0.001). Similar result was seen among females (IRR = 1.04 (1.03-1.04); p < 0.001). In early adulthood, there was significant increase among females (IRR = 1.04 (1.03-1.05); p < 0.001), but among males, the change was not significant (IRR = 0.99 (0.99-1.00), p = 0.051). Conclusions The main finding was that the cumulative incidence of hospital-treated psychiatric disorders increased over the decades in Finland. The increasing trend in hospital-treated psychiatric disorders in early adulthood was detected in females but not in males. In the youngest cohorts, the cumulative incidence of hospital-treated psychiatric disorders was at the same level in males and females, whereas in oldest cohort, males had higher incidence than females.