Early development in children that are later diagnosed with disorders of attention and activity: a longitudinal study in the Danish National Birth Cohort.

Not much is known about the early development in children that are later diagnosed with disorders of attention and activity (ADHD). Using prospective information collected from mothers in the Danish National Birth Cohort (DNBC), we investigated if developmental deviations in the first years of life are associated with later ADHD. In the DNBC 76,286 mothers were interviewed about their child's development and behaviour at age 6 and 18 months. At the end of follow-up, when the children were 8-14 years of age, 2034 were registered in Danish health registers with a clinical diagnosis of ADHD. The Hazard Ratio of ADHD was estimated using Cox regression model. At 6 months of age deviations in development showed associations with the child later being diagnosed with ADHD such as duration of breastfeeding, motor functioning, and incessant crying. At 18 months, many observations clearly associated with ADHD as for example the child not being able to fetch things on request [HR 3.0 (95 % CI 2.4; 3.7)], or the child being significantly more active than average [HR 2.0 (95 % CI 1.8; 2.2)]. An association to ADHD was shown, especially at 18 months, if the mother found it difficult to handle the child [HR 2.9 (95 % CI 2.4-3.5)]. However, it goes for all observations that the positive predictive values were low. Many children with ADHD showed signs of developmental deviations during the first years of their life. In general, however, ADHD cannot be identified solely on basis of the questions in DNBC.