Smoking during pregnancy and hyperactivity-inattention in the offspring--comparing results from three Nordic cohorts.
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.


CONCLUSIONS
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.
Obel
Carsten
C
The Perinatal Epidemiology Research Unit, Department of Obstetrics, Aarhus University Hospital, Skejby, Denmark. co@soci.au.dk;co@alm.au.dk
Linnet
Karen Markussen
KM
Henriksen
Tine Brink
TB
Rodriguez
Alina
A
Järvelin
Marjo Riita
MR
Kotimaa
Arto
A
Moilanen
Irma
I
Ebeling
Hanna
H
Bilenberg
Niels
N
Taanila
Anja
A
Ye
Gan
G
Olsen
Jørn
J
D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology* / Q000235:genetics; D001294:Attitude to Health; D002648:Child; D015986:Confounding Factors, Epidemiologic; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D006948:Hyperkinesis / Q000453:epidemiology* / Q000235:genetics; D008297:Male; D009035:Mothers; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000453:epidemiology* / Q000235:genetics; D015995:Prevalence; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology / Q000235:genetics; D011795:Surveys and Questionnaires