A fetus is more likely to have chromosomal instability, expressed as an increase in structural chromosomal abnormalities and chromosomal lesions, when a woman smokes 10 or more cigarettes a day for at least 10 years and continues to smoke during pregnancy. And that danger is not influenced by maternal age. 

The findings come from a prospective study of 50 women (25 controls and 25 smokers) in Spain. Structural chromosomal abnormalities occurred almost 3.5 times as frequently in the amniotic cells of smokers as compared with nonsmokers (12.1% vs. 3.5%, respectively, 

=0.002). The differences concerning chromosomal instability (10.5% for smokers vs. 8.0% for nonsmokers, 

=0.04) and chromosomal lesions (15.7% vs. 10.1%, respectively, 

It seems exposure to tobacco increases chromosomal instability by delaying or interfering with DNA replication or repair mechanisms, both of which affect the integrity of chromosomal structure and lead to structural chromosomal abnormalities, gaps, and breaks. One chromosome band that seems particularly vulnerable to damage by tobacco is 11q23, which is associated with childhood leukemia.  

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A fetus is more likely to have chromosomal instability, expressed as an increase in structural chromosomal abnormalities and chromosomal lesions, when a woman smokes 10 or more cigarettes a day for at least 10 years and continues to smoke during pregnancy. And that danger is not influenced by maternal age.