For most of the pathologies mentioned, there is a dose-effect relationship, i.e. the risk of a given pathology increases with the number of cigarettes smoked.

Recent studies indicate that children born at normal weight, despite prenatal exposure to tobacco smoke, may experience other distant effects in the form of increased risk of bronchial asthma and neuro-behavioural developmental disorders.

Studies that systematically collected information on the health status of children of mothers who smoked during pregnancy found that their children were more likely to develop chronic bronchitis and wheezing than children of non-smoking mothers, and had an approximately 30 per cent increased risk of bronchial asthma, the prevalence of which was steadily increasing anyway. Interestingly, research conducted in California, USA, indicates that not only do the children of mothers who smoke during pregnancy have an increased risk of asthma, but also the children of non-smoking mothers whose grandmothers smoked during pregnancy.

These data suggest that smoking during pregnancy is likely to cause changes in the foetus by disrupting the expression of genes relevant to asthma pathology. These are known as epigenetic effects. Epigenetics deals with the study of inherited traits that do not depend on the original DNA sequence. Epigenetic studies are mainly concerned with: DNA methylation (the process of attaching methyl groups (-CH3) to nitrogenous bases), especially to cytosine, less frequently to adenine, modifications of histone proteins and changes in chromatin structure. Children of women who smoked 10 or more cigarettes a day during pregnancy had difficulty learning to read and also performed worse in science subjects.

It was also observed that children of women who smoked 10 or more cigarettes per day scored lower on the Stanford-Binet scale test of intellectual development. Other findings indicate that smoking during pregnancy can cause, through the epigenetic changes already mentioned, attention deficit hyperactivity disorder (ADHD). This is characterised by symptoms of hyperactivity, impulsivity and attention deficit disorder. Interestingly, adolescents and adults with ADHD syndrome in childhood are more likely to smoke cigarettes in adulthood.

Thus, the smoking habit is passed on to the next generation. In conclusion, it is important to emphasise that smoking by pregnant women not only means a smaller baby, but also a significantly increased risk of many obstetric complications, as well as distant health effects negatively affecting quality of life both in adolescence and adulthood.

References: 1. Li, Y, Langholz B, Salam M T, Gillard FD. Maternal and grandmaternal smoking pattterns are associated with early childhood asthma. Chest 2005, 127, 1232-1241

2. Neuman R J, Lobos, E Reich W, Henderson CA, Sun , Todd RD. Prenatal smoking exposure and dopaminergic genotypes interact to cause a severe ADHD subtype. Biol Psychiatry 2007, 61, 1320-1328