Over the past two decades, the number of people with asthma in the US has more than doubled, to its present figure of more than 20 million. While asthma can develop at any age, it most commonly sets in during early childhood and is a common cause of missed school days.

In asthma, sensitivity to allergens and irritations leads to chronic inflammation of the airways in the lungs. During an asthma attack, the airways constrict, resulting in symptoms such as wheezing, breathlessness, coughing, and chest tightness.

Although it is not known what causes asthma, family history is a significant risk factor: an individual with a parent who has asthma is 3–6 times more likely to develop asthma than an individual who does not have a parent with asthma. Evidence also suggests that children born to mothers who smoked during their pregnancies are more likely to develop asthma.

A new study, published in the April 2005 issue of CHEST , set out to more closely examine the effects of smoking before, during, and after pregnancy on asthma occurrence. In addition to looking at the smoking patterns of the mothers, the researchers also examined the smoking habits of the maternal grandmothers. Their results showed that if a child’s maternal grandmother smoked during pregnancy, that child was almost twice as likely to develop asthma as a child whose maternal grandmother did not smoke.

About the Study

This study included 279 children who had been diagnosed with asthma during the first five years of life, and 412 children without asthma who were similar to the asthma group in age, sex, and community of residence. These children were recruited from a subset of the Southern California Children’s Health Study.

The researchers interviewed the mothers (or other guardians when necessary) of these children regarding smoking status, and amount smoked before, during, and after pregnancy. They also asked about the smoking habits of the maternal grandmother of each participating child and interviewed a subset to make sure that their responses were accurate. Additionally, they gathered information on secondhand smoke exposure, including the number of household smokers and their relationship to the child.

The Findings

Children with both a mother and maternal grandmother who smoked during pregnancy were 2.6 times more likely to develop asthma when compared to children whose mother and maternal grandmother did not smoke during pregnancy. If only the mother smoked, children were 1.3 times more likely to develop asthma, and if only the maternal grandmother smoked, children were still 1.8 times more likely to develop asthma.

Children with mothers who quit smoking before their pregnancy did not have an increased risk of developing asthma. However, the authors could not determine the effect of quitting smoking during the first trimester of pregnancy as very few mothers reported having done so. Interestingly, heavier smoking during pregnancy did not significantly increase asthma risk, nor did exposure to secondhand smoke after birth.

How Does This Affect You?

This study suggests that smoking during pregnancy may cause lasting harmful effects that are sometimes not apparent until future generations. It is the first study to show that smoking during pregnancy may not only affect the child’s risk of developing asthma, but also the future grandchild’s risk. The researchers note that one potential explanation for these results is that tobacco affects the DNA of the fetus, which is then passed onto the next generation.

This is a novel study, with many limitations that raise questions about its findings. Additional studies are needed to back up these results and to find out whether there is a specific time during pregnancy when exposure results in an increased risk of asthma.

If the results of this provocative study are confirmed, smoking can apparently harm the lives of generations to come. This effect can be added to a long list of other conditions linked to smoking before, during, and after pregnancy, including ectopic pregnancy , spontaneous abortion , stillbirth, and SIDS (sudden infant death syndrome) . Perhaps this will be enough to motivate some smokers to get the help they need to quit once and for all.