Despite the fact that smoking during pregnancy has been associated with SIDS, miscarriage, low birth weight, and reduced lung function, 12% of pregnant women in the United States smoke. Perhaps the findings published in a new report in the American Journal of Human Genetics will persuade them to think seriously before lighting up. The report culled together data from 13 birth studies and found that DNA methylation (or places that reflect chemical modifications in the DNA) occurred in 6073 sites in the children born from regular smokers. Many of these DNA changes were in genes related to cleft lip or palate, lung and nervous system development, cancers (including those that are typically smoking-related), and autism spectrum disorders. Several of the DNA differences found in the babies mirrored the changes that also typically exist in the DNA of adult smokers. Although the study’s authors had less information regarding long-term effects on children born from a mother who smoked, an analysis did find that some of these DNA changes persisted into older childhood. The study found that any smoking during pregnancy had an effect on DNA methylation, and that this effect was particularly significant when a mother smoked throughout the course of her pregnancy. The report, which analyzed the newborns’ DNA using umbilical blood samples after delivery, included data from 6,685 babies. 13% were born from mothers who were daily smokers, while an additional 25% were born from mothers who reported smoking occasionally during pregnancy. While further research is planned to explore the links between these gene changes and disease, this report provides more than 6,000 reasons for pregnant women to do themselves and their fetus a big, giant favor and put that cig down.