There is a significant association between maternal smoking during pregnancy and offspring conduct problems, researchers in Britain say. Professor Gordon Harold and Dr. Darya Gaysina, of the University of Leicester in England, and colleagues in the United States and New Zealand, examined the relationship between maternal smoking during pregnancy and offspring conduct problems among children raised by genetically related mothers and genetically unrelated mothers. In the meta-analysis, the researchers used three studies: the Christchurch Health and Development Study, a longitudinal study that includes biological and adopted children; the Early Growth and Development Study, a longitudinal adoption-at-birth study; and the Cardiff In Vitro Fertilization Study, an adoption-at-conception study among genetically related families and genetically unrelated families. Maternal smoking during pregnancy was measured as the average number of cigarettes per day smoked during pregnancy. The study, published in the Journal of the American Medical Association Psychiatry, found smoking during pregnancy appeared to be a prenatal risk factor associated with conduct problems in children. \"Our findings suggest an association between pregnancy smoking and child conduct problems that is unlikely to be fully explained by post-natal environmental factors such as parenting practices even when the post-natal passive genotype-environment correlation has been removed,\" the authors concluded.