Maternal smoking during pregnancy and childhood cancer

The association between maternal smoking during pregnancy and childhood cancer was investigated using prospectively collected data from 54,795 liveborn children in the Collaborative Perinatal Project (1959-1966). Cases of cancer had a histologic diagnosis and/or a compatible clinical course. There were 51 children with cancer, for a cumulative incidence of cancer of 1.1 per 1,000 by 96 months of age. Maternal smoking was determined at each prenatal visit; 52% of mothers reported smoking at one or more visits. By age 8 years, cancer had occurred in 1.4 per 1,000 children whose mothers did not smoke during pregnancy, compared with 0.9 per 1,000 children whose mothers smoked (p = 0.15 by log rank test); the hazard ratio was 0.67 (95% confidence interval (CI) 0.38-1.17). There was no dose-response effect of smoking compared with nonsmokers (hazard ratio for one to 10 cigarettes/day = 0.45, more than 10 cigarettes/day = 0.83). The hazard ratio for leukemia among children whose mothers smoked was 0.82 (95% CI 0.31-2.11); the hazard ratio for cancers other than leukemia was 0.60 (95% CI 0.30-1.20). Adjustment did not change the hazard ratio substantially. Although the relatively small number of cases precluded extensive study of individual types of cancer, the authors conclude that maternal smoking during pregnancy is not associated with an increased risk of childhood cancer in this cohort.