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AIMS: To study the association between gestational age and birth weight and the risk of clinically verified hyperkinetic disorder. METHODS: Nested case-control study of 834 cases and 20 100 controls with incidence density sampling. RESULTS: Compared with children born at term, children born with gestational ages of 34-36 completed weeks had a 70% increased risk of hyperkinetic disorder (rate ratio (RR) 1.7, 95% confidence interval (CI) 1.2 to 2.5). Children with gestational ages below 34 completed weeks had an almost threefold increased risk (RR 2.7, 95% CI 1.8 to 4.1). Children born at term with birth weights of 1500-2499 g had a 90% increased risk of hyperkinetic disorder (RR 1.9, 95% CI 1.2 to 2.9), and children with birth weights of 2500-2999 g had a 50% increased risk (RR 1.5, 95% CI 1.2 to 1.8) compared with children born at term with birth weights above 2999 g. The results were adjusted for socioeconomic status of the parents, family history of psychiatric disorders, conduct disorders, comorbidity, and maternal smoking during pregnancy. Results related to birth weight were unchanged after adjusting for differences in gestational age. CONCLUSIONS: Children born preterm, also close to term, and children born at term with low birth weights (1500-2499 g) have an increased risk of clinically verified hyperkinetic disorder. These findings have important public health perspectives because the majority of preterm babies are born close to term.

AIM: To study the association between intrauterine exposure to tobacco smoke and behavioural disorders in preschool children, primarily symptoms of inattention, hyperactivity and impulsivity but also hostile-aggressive and anxious-fearful symptoms. METHODS: We conducted a follow-up study in 1355 singletons born to Danish-speaking mothers. Information on smoking habits during pregnancy and other lifestyle factors was obtained from self-administered questionnaires filled in during second and third trimester. Approximately 3.5 years later, the parents provided information on their child's behaviour using the self-administered Preschool Behaviour Questionnaire. The children were categorized into three not mutually exclusive behaviour groups: hyperactive - distractible (13.6%), hostile-aggressive (4.6%), and anxious-fearful (6.4%) children. RESULTS: Compared with children of non-smokers, children born to women who smoked 10 or more cigarettes per day had a 60% increased risk of hyperactivity and distractibility perceived by the parents (OR 1.6; 95% CI 1.0-2.3; P < 0.05). The results were adjusted for maternal lifestyle factors and socioeconomic characteristics. Additional adjustment for perinatal factors and parental psychiatric hospitalization did not change the results substantially (OR 1.7; 95% CI 1.1-2.6). We found no statistically significant association between maternal smoking in pregnancy and hostile-aggressive and anxious-fearful behaviour in the offspring. CONCLUSION: Exposure to tobacco smoke in utero was associated with hyperactive-distractible behaviour in preschool children.

Background: Studies concerning whether exposure to low levels of maternal alcohol consumption during fetal development is related to child inattention and hyperactivity symptoms have shown conflicting results. We examine the contribution of covariates related to social adversity to resolve some inconsistencies in the extant research by conducting parallel analyses of three cohorts with varying alcohol consumption and attitudes towards alcohol use. Methods: We compare three population-based pregnancy–offspring cohorts within the Nordic Network on ADHD from Denmark and Finland. Prenatal data were gathered via self-report during pregnancy and birth outcomes were abstracted from medical charts. A total of 21,678 reports concerning inattention and hyperactivity symptoms in children were available from the Strengths and Difficulties Questionnaire or the Rutter Scale completed by parents and/or teachers. Results: Drinking patterns differed cross-nationally. Women who had at least some social adversity (young, low education, or being single) were more likely to drink than those better off in the Finnish cohort, but the opposite was true for the Danish cohorts. Prenatal alcohol exposure was not related to risk for a high inattention-hyperactivity symptom score in children across cohorts after adjustment for covariates. In contrast, maternal smoking and social adversity during pregnancy were independently and consistently associated with an increase in risk of child symptoms. Conclusions: Low doses of alcohol consumption during pregnancy were not related to child inattention/hyperactivity symptoms once social adversity and smoking were taken into account.

Background Prenatal exposure to smoking has been associated with Attention Deficit Hyperactivity Disorder (ADHD) in a number of epidemiological studies. However, mothers with the ADHD phenotype may ‘treat’ their problem by smoking and therefore be more likely to smoke even in a society where smoking is not acceptable. This will cause genetic confounding if ADHD has a heritable component, especially in populations with low prevalence rates of smoking since this reason for smoking is expected to be proportionally more frequent in a population with few ‘normal’ smokers. We compared the association in cohorts with different smoking frequencies. Methods A total of 20 936 women with singleton pregnancies were identified within three population-based pregnancy cohorts in Northern Finland (1985–1986) and in Denmark (1984–1987 and 1989–1991). We collected self-reported data on their pre-pregnancy and pregnancy smoking habits and followed the children to school age where teachers and parents rated hyperactivity and inattention symptoms. Results Children, whose mothers smoked during pregnancy, had an increased prevalence of a high hyperactivity-inattention score compared with children of nonsmokers in each of the cohorts after adjustment for confounders but we found no statistical significant difference between the associations across the cohorts. Conclusion The estimated association was not strongest in the population with the fewest smokers which does not support the hypothesis that the association is entirely due to genetic confounding.

Objectives: We examine whether pregnancy weight (pre-pregnancy body mass index (BMI) and/or weight gain) is related to core symptoms of attention deficit hyperactivity disorder (ADHD) in school-age offspring. Design: Follow-up of prospective pregnancy cohorts from Sweden, Denmark and Finland within the Nordic Network on ADHD. Methods: Maternal pregnancy and delivery data were collected prospectively. Teachers rated inattention and hyperactivity symptoms in offspring. High scores were defined as at least one core symptom rated as ‘severe’ and two as ‘present’ (approximately 10% of children scored in this range). Logistic regression and latent class analyses were used to examine maternal pregnancy weight in relation to children's ADHD core symptoms. Results: Teacher rated 12 556 school-aged children. Gestational weight gain outside of the Institute of Medicine guidelines was not related to ADHD symptoms (below recommendations: odds ratio (OR): 0.96; 95% confidence interval (CI): 0.81, 1.14; above recommendations: OR: 0.98; 95% CI: 0.82, 1.16). To examine various patterns of pre-pregnancy BMI and weight gain, we used latent class analysis and found significant associations between classes that included pre-pregnancy overweight or obesity and a high ADHD symptom score in offspring, ORs ranged between 1.37 (95% CI: 1.07, 1.75) and 1.89 (95% CI: 1.13, 3.15) adjusted for gestational age, birth weight, weight gain, pregnancy smoking, maternal age, maternal education, child gender, family structure and cohort country of origin. Children of women who were both overweight and gained a large amount of weight during gestation had a 2-fold risk of ADHD symptoms (OR: 2.10, 95% CI: 1.19, 3.72) compared to normal-weight women. Conclusions: We show for the first time that pre-pregnancy BMI is associated with ADHD symptoms in children. Our results are of public health significance if the associations are causal and will then add ADHD symptoms in offspring to the list of deleterious ou