Aim: We examined the associations between preterm birth, poor foetal growth and anxiety disorders among children and adolescents. Additionally, we examined the im-pact of common comorbidities and specific anxiety disorders separately.

Methods: Three  Finnish  registers  provided  data  on  a  nationwide  birth  cohort  of  22,181 cases with anxiety disorders and 74,726 controls. Conditional logistic regres-sion was used to examine the associations.

Results: Extremely very preterm birth and moderate- late preterm birth were associ-ated with increased adjusted odds ratios (aOR) for anxiety disorders (aOR 1.39, 95% CI  1.11–1.75  and  aOR  1.13,  95%  CI  1.03–1.23,  respectively).  Weight  for  gestational  age of less than −2SD (aOR 1.29, 95% CI 1.17–1.42) and −2SD to −1SD (aOR 1.08, 95% CI 1.03–1.14) were associated with increased odds ratios for anxiety disorders. When comorbidities were considered, the associations became statistically insignificant for pure anxiety disorders, but remained significant in the groups with comorbid depres-sive or neurodevelopmental disorders.

Conclusion: Preterm birth and poor foetal growth increased the odds for anxiety dis-orders. However, the associations seem to be explained by the conditions of comorbid depressive  and  neurodevelopmental  disorders.  Comorbidities  should  be  considered  when examining and treating child and adolescent anxiety disorders.