There have been numerous studies that have highlighted the link between mothers smoking while they are pregnant and their children developing behavioural or learning difficulties. The problem for many of these studies remains the complicated interrelationship between genetics and environment, which makes it difficult to precisely pinpoint the cause of certain problems in later life. Even though some of these causal relationships have yet to been clearly defined, the fact remains that smoking has many detrimental effects on infants.It is well established that smoking can have many adverse effects on babies during pregnancy. Prenatal smoking can result in miscarriage, premature births, low birth weights for babies, infant mortality, and obstetric complications. The babies of pregnant mothers who smoke have been shown to have a smaller head circumference and are shorter in length than the babies of non-smokers. One Finnish report noted that the children of prenatal smokers tended to be almost one centimetre shorter than those children with mothers that did not smoke. The smoking mother's child was also considered more likely to develop respiratory diseases.Although the research is inconclusive, smoking appears to carry an increased risk sudden infant death syndrome (SIDS), or "cot death" in babies. It should not be forgotten that smoking while pregnant actually reduces your chances of becoming pregnant in the first place because it reduces fertility in women, disrupts the menstrual cycle and can lead to early menopause.Despite all of the information that is available about the damaging effects of smoking, to both the mother and the child, it has been estimated that approximately 20% to 25% of pregnant women will still continue to smoke while pregnant. One study observed that up to 30% of women in urban, non-ghetto regions of the United States admitted to having smoked during pregnancy.One of the suspected results of this prenatal smoking is hyperactivity in some babies. A study into this phenomenon by Professor Christopher and colleagues at Gotenburg University in Sweden found that smoking could cause neurological disorders in babies. The study involved a sample 62 six-year-old Swedish children and included a control group of healthy children without deficit disorders. The results showed that those children who had been exposed to prenatal smoking while in the womb were more prone to experiencing learning difficulties and developing conditions such as attention deficit disorder (ADD) or attention deficit hyperactivity disorder (ADHD). Another term used to describe the problems more common amongst this group of children is DAMP, or deficits in attention, motor control and perception.This Swedish study estimated that the rate of deficit disorders amongst the children of mothers who smoked during pregnancy was twice that of the healthy children. Additionally, the children of prenatal smokers where found to be more likely to suffer stomach and sleep problems and approximately two-thirds of these children had language difficulties. At least one other Scandinavian study concurred that there was a link between ADD and prenatal exposure to tobacco smoke. Another study involving twins at the Washington University School of Medicine in St. Louis found that children with a particular type of attention deficit-hyperactivity disorder (ADHD) were actually at an increased risk of starting smoking because some considered this an option for reducing the symptoms of their disorder.Another Swedish study, undertaken by Dr Christina Hultman and researchers from the Department of Medical Epidemiology at the Karolinska Institutet in Stockholm, Sweden, studied over 2000 children with regards to the link between prenatal smoking and autism. They discovered that, because smoking affects the growth of the foetus in the womb and lowers the birth weight of babies, mothers who smoke were 40% more likely to have an autistic child than non-smokers were.Prenatal smoking has also been linked to some children's poor performance in school. Research into this phenomenon is not a recent development. Dr. R. Butler and Dr. H. Goldstein, from the Bristol Royal Hospital for Sick Children, published an article in the British Medical Journal in 1973 outlining results from what was known as the National Child Development Study in Britain. Involving over 9000 children, it measured the affects of the child's mother smoking 0, 10, or more than 10 cigarettes a day during pregnancy. At the ages of seven and eleven, the children's physical measurements were recorded and they were given tests to evaluate their abilities in mathematics and reading. The results showed that if a mother smoked more than 10 cigarettes a day while pregnant then her child was, on average, one centimetre shorter and between three and five months behind in reading, mathematics, and general ability when compared to the child of a non-smoker.The Department of Public Health, at Oulu University, Finland, studied a sample of 1,819 women who smoked during pregnancy. In the early 1980's, a follow up study examined those children who had reached the age of 14 years. The researchers concluded that the school performance and mean ability of those children whose mothers smoked during pregnancy was poorer than the children of non-smoking mothers, irrespective of factors such as gender or social class.Researchers at the Department of Psychology at Carleton University in Ottawa, Canada, tested 91 children between the ages of six and nine years of age on a wide range of developmental, academic and behavioural skills to see what effect prenatal smoking had on children. The tests covered speech and language skills, intelligence, mathematical ability, visual/spatial abilities, and the mother's rating of their child's behaviour in a questionnaire. The results of the study, led by Dr. Judy Makin and Dr. Peter A. Fried, were published in Neurotoxicology and Teratology, Volume 13, 1991. They showed that the children of non-smoking mothers were generally found to perform better in each of the tests than the children from the two smoking groups, separated into 'active' and 'passive' smoking classifications. The children with non-smoking mothers were observed to have the best attention and co-operation skills, while the children of active smoking mothers were more likely to be perceived as having problems in school.A longitudinal study, undertaken at Brisbane Mater Hospital in Australia and involving 4879 five-year-old children who were the children of mothers who were patients at the hospital, examined the link between smoking and pregnancy. Care was taken by researchers to eliminate other possible factors and only compare smokers and non-smokers with similar backgrounds to ensure the integrity of the results. The results suggested that mothers who smoke early in the pregnancy are putting their children at twice the normal risk of developing behavioural problems.The amount of risk was relative to the amount that she smoked so that the more she smoked, the greater the apparent risk her child would develop behavioural difficulties. The early period within the womb is a critical time in the development of a baby's nervous system and the components of tobacco were able to cross the placenta from mother to child during this time. The association between prenatal smoking and developmental problems in children was considered "quite strong" according to Professor Jake Najman, the study's co-author. It was these children who were considered more prone to aggressive or delinquent behaviour as they grew up.Other researchers have turned their attention to the amount that the mother smoked while pregnant. The St. Petersburg State Paediatric Medical Academy studied the relationship between maternal smoking during pregnancy and the behavioural characteristics in two to four month old infants. The study incorporated 250 randomly selected children, 129 boys and 121 girls, all apparently healthy. About 25.6% of the mothers involved in the study had smoked during pregnancy. The children of these mothers were more likely to exhibit fussy behaviour, were more excitable, were less attentive to parents during playful interaction, were more demanding and harder to console when upset. In other words they generally displayed more intense reactions in their behaviour, both positive and negative. The association between prenatal smoking and behavioural deviations in infants was considered to have a "dose-response" component with the risk to the infant being higher the more the mother smoked.An article examining the effects of prenatal smoking on the conduct of boys appeared in the July 1997 issue of Archives of General Psychiatry. The study was organised by researchers from the University of Chicago Medical Center and the University of Pittsburgh. It involved the analysis of the records of 177 boys aged from 7 to 12 years of age who had been referred to outpatient clinics because of behavioural problems. As Lauren S. Wakschlag, Ph.D., the lead author of the study, stated "Our study indicates that regardless of other risk factors, smoking during pregnancy can have serious behavioural outcomes for children". The researchers found that the risk of boys developing conduct disorder (CD) was approximately four times greater for the children of mothers who smoked at least 10 cigarettes a day while pregnant. Conduct disorder is defined by chronic, serious anti-social behavioural problems, including vandalism, bullying, and theft. A separate study involving more than 5000 children suggested that smoking during pregnancy roughly doubled the risk of children displaying aggressive behaviour when five years old.The link between prenatal smoking and behavioural difficulties in children was the subject of a University of Chicago study. The study followed 77 African-American inner city youths, from infancy to adolescence, and reinforced the belief that prenatal smoking causes "neurobehavioural difficulties" in infants. Researchers Lauren S. Wakschlag Ph.D. and Sydney L. Hans Ph.D. presented data suggesting that children exposed to prenatal smoking were more likely to exhibit symptoms of anti-social behaviour before they reached ten years of age.Researchers from the Institute of Psychiatry at King's College in London conducted interviews with the mothers of over 1,100 sets of identical and non-identical twins to find other whether they had smoked during pregnancy and what their child's behaviour patterns were at home. After eliminating other social factors such as poverty and social class, the study discovered that if a mother smoked more than 20 cigarettes a day during pregnancy then their child was more likely to exhibit disruptive or anti-social behaviour.While the exact reason for this was unclear, one hypothesis was that smoking affected the developmental genes involved in the growth of the foetal brain in unborn children. In an article in Neurotoxicology and Teratology, Dr. T. S. Roy of the Department of Anatomy at the All India Institute of Medical Sciences, New Delhi, India, reported that prenatal nicotine exposure in laboratory rats had resulted in physiological changes in their cerebral cortex. The observable results included significantly reduced thickness of the cerebral cortex, small cerebral cortex neurons, and overall reduced brain weight. The study also reinforced the idea that these effects were dose dependent.However, not all published studies have agreed with the findings that link prenatal smoking to behavioural difficulties in children. A study undertaken at the Virginia Institute for Psychiatric and Behavioural Genetics at Virginia Commonwealth University (VCU) and published in Biological Psychiatry hypothesized that the dynamics of the link between prenatal smoking and adolescent behavioural problems lay with the mother's own "anti-social" behaviour. The suggestion is that the anti-social behaviour of the mother herself has more impact on the behavioural problems of the child than smoking. In arguing this, the study appears to be in conflict with the findings of the many other studies that link prenatal smoking with behavioural difficulties in children.The VCU investigation involved data from 538 adolescent twin boys aged 12 to 17 years of age. These twins participated in the Virginia Twin Study of Adolescent Behavioural Development, a 15-year study into the role of genetic and social factors in the development of psychiatric problems in children and adolescents. The study concentrated on what it referred to as "sub-threshold conduct disorders". These were defined as things like fighting, lying, starting fires, and other consistent behaviour indicative of belligerence, disobedience, and a general disregard for other people.The study's author, Assistant Professor Judy L. Silberg, stated "You might hypothesize that a woman who smokes during her pregnancy . . . it says something about her". Rather than blaming smoking as a cause, the study sees smoking as a sign of the mother's anti-social behaviour and suggests that these behavioural patterns are passed to their children, leading them to develop their own anti-social tendencies. Part of the argument is that if a mother smokes while pregnant, despite all the evidence that it is harmful to the baby, then questions can be asked about whether the well-being of the child is paramount and what implication this has for the standard of motherhood. The mother's own anti-social behaviour can make her smoke during pregnancy and, the study maintains, it is this anti-social tendency that is passed on to her child, causing subsequent behavioural problems.In making these claims, the VCU study does not deny that prenatal smoking is harmful but rather does not necessarily see the relationship between smoking and later behavioural problems in children as one of cause and effect. It recognises that further study is required to discover whether the prime influence in the behavioural component was genetic or environmental.The issue is certainly complicated. Take for example other studies that have outlined how mothers who suffer from anxiety or depression during pregnancy may increase the chances that their children will experience behaviour problems, including ADD, anxiety and depression. Like smoking, stress and anxiety are also risk factors for premature birth or low birth weights, both of which have been linked to children's behavioural problems. The two are interrelated because smoking is believed to increase the level of stress and tension in a baby relative to the amount smoked.It has been estimated that mothers who are very anxious during pregnancy, especially in the later months, almost doubled the chances that their child would have severe emotional or behavioural problems. People who are prone to anxiety often smoke in an attempt to alleviate their symptoms so anxiety disorders may play a role in them smoking in the first place. The question then becomes how much smoking is merely symptomatic of existing problems that may be passed on to a child and how much smoking is a causal factor in later difficulties experienced by the child.Smoking whilst pregnant suggests a certain degree of disregard for the well-being of the child but whether this is indicative of anti-social tendencies by the mother is open to debate. On a sociological level, however, the fact that a mother is risking premature death by smoking, potentially depriving their child of parental guidance may not bode well for the behavioural stability of the child.While the causal relationship between prenatal smoking and behavioural problems in children may be unclear, there is plenty of evidence to show a correlation between smoking and behavioural or learning difficulties in children. For example, smoking has been shown to lower birth weights and these babies are more prone to intellectual and developmental problems such as learning disabilities, visual and hearing difficulties, and delayed speech. If the mother smoked while pregnant then it is highly likely that the child will also be exposed to dangerous amounts of passive smoking during their early developmental years. It certainly seems clear from all this research that smoking puts a child at greater risk of health problems and that these developmental difficulties have implications for their learning and behavioural tendencies.