The March 5, 2005 issue of the British Medical Journal reports on a study that shows that mothers who smoke in late pregnancy risk having children with lower intelligence. The research found that young men whose mothers smoked 20 or more cigarettes a day had IQs that were on average 6.2 points below those of sons of non-smokers.
The study noted that the more the mother smoked, the more it affected IQ of the offspring when they grew to an adult. Additionally, the study noted that there was no real difference in socio-economic levels related to the loss of IQ and smoking during late pregnancy.
Erik Mortensen, researcher and one of the authors from Copenhagen University Hospital, Indiana University, commented, "Our results reveal significant long term effects of maternal smoking during pregnancy on mental development. Maternal smoking during pregnancy was associated with lower adult intelligence and there appeared to be a dose-response relationship between maternal smoking and offspring intelligence."
The study noted that the reason for this finding was not totally understood, but the authors did say an adverse effect on the central nervous system and brain may be a factor: "It seems justified to assume that part of the effect of maternal smoking on offspring cognitive development is a direct result of the effect of substances in cigarette smoke on the fetal central nervous system.