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Background Conventional cohort studies have consistently shown that exposure to maternal smoking in pregnancy is associated with about twice the risk of attention deficit hyperactivity disorder (ADHD) in the offspring. However, recent studies using alternative designs to disentangle the effect of social and genetic confounders have suggested that confounding may account for the association. In this study we aimed to estimate the association by a sibling design. Methods We used a design with half and full siblings in a Danish national register-based cohort on all singletons born between January 1991 and December 2006 and followed until January 2011. Data were available for 90% ( N = 968,665) of the singleton live births in the period. We used the combination of the International Classification of Diseases (10th version) diagnosis of hyperkinetic disorder (HKD) and ADHD medication to identify children. We used sibling-matched (conditional) Cox regression to control social and genetic confounding. Results Using conventional cohort analyses, we found the expected association between pregnancy smoking and offspring ADHD (adjusted HR 2.01, 95% CI 1.94-2.07). In the sibling analysis, however, we did not detect such a strong association (adjusted HR 1.07, 95% CI 0.94-1.22). There was no difference between results for half- and full sibling analyses. The link between pregnancy smoking and low birth weight remained robust in the sibling design (adjusted OR 1.68, 95% CI 1.33-2.12). Conclusions We found no support for prenatal smoking as a strong causal factor in ADHD. Our findings suggest that the strong association found in most previous epidemiological studies is likely to be due to a strong link between maternal smoking and maternal ADHD genetics or shared family environment. Pregnant women should still be encouraged to stop smoking because of other risks, but we have no reason to believe that this would reduce the risk of ADHD in the offspring. [ABSTRACT FROM AUTHOR]

The article reports a study which examined whether the onset of rheumatoid arthritis (RA) in women before conception affects the time to pregnancy (TTP). It mentions that the study evaluated pregnant women who enrolled in the Danish National Birth Cohort between 1996 and 2002, and used the Danish National Hospital Discharge Registry to identify women with RA. Details pertaining to the methods, data analysis and study results are also presented.

Today, most persons with Down syndrome (DS) survive into middle age, but information on their social conditions as adults is limited. We addressed this knowledge gap using data from national registers in Denmark. We identified a national cohort of 1,998 persons with DS who were born between 1968 and 2007 (1,852 with standard trisomy 21, 80 with Robertsonian translocations and 66 with mosaicism) using the Danish Cytogenetic Register. We followed this cohort from 1980 to 2007. Information on social conditions (education, employment, source of income, marital status, etc.) was obtained by linkages to national registers, including the Integrated Database for Longitudinal Labor Market Research. For those aged 18 and older, more than 80% of persons with DS attended 10 years of primary school, with about 2% completing secondary or post-secondary education. About 4% obtained a full-time job, whereas the remaining mainly received public support from the government. Only a few (1-2%) of persons with DS were married or had a child. No significant differences in these social conditions were seen between males and females. More persons with mosaic DS attended secondary or post-secondary education, had a full-time job, were married, or had a child (18%, 28%, 15%, and 7%, respectively), compared with persons with standard DS (1%, 2%, 1%, and 1%, respectively). These data may provide families with better insight into social conditions and society with a better understanding of the social support needed for persons with DS., (© 2013 Wiley Periodicals, Inc.)

Most persons with Down syndrome (DS) now survive to adulthood, but their health care needs beyond childhood are not well described. We followed a national cohort of 3,212 persons with DS and a reference cohort of persons without DS through the Danish National Hospital Register from January 1, 1977, to May 31, 2008. Poisson regression was used to calculate rate ratios for numbers of overnight hospital admissions and hospital days. During the study period, persons with DS had more than twice the rate of hospital admissions and nearly three times as many bed-days as the population as a whole. Malformations, diseases of the respiratory system, and diseases of the nervous system or sensory organs were the principal indications for hospital admissions. The higher rate ratios for hospital admissions were seen especially among persons less than 20 years of age. Hospitalizations for neoplasms or for diseases of the musculoskeletal system or connective tissue were much less frequent among adults with DS. As survival among persons with DS continues to improve, these findings are likely to be useful for health care planning, although the potential utility may be different for different health care systems., (Copyright © 2013 Wiley Periodicals, Inc.)