Motivated by concern for the health of their babies (2), women are more likely to quit smoking in pregnancy than at any other time (17). However, many pregnant women continue to smoke. Our data support the role of genetic factors in predisposing to this detrimental behavioural phenotype. The association is not deterministic: approximately one-third of women carrying two copies of the risk allele did quit smoking in pregnancy. However, the 1.66-fold (95% CI 1.21–2.26) higher odds of continued smoking in women with two risk alleles (11% of the total) versus women with none (44%) is a strong evidence that the polymorphism is a susceptibility factor for an important human behavioural trait. This may have implications for the design of interventions to help women quit smoking in pregnancy, and possibly for smoking cessation strategies more generally. It will be important to investigate this possibility.
