OBJECTIVE: Studies of the effect of maternal smoking during pregnancy on 
development of brain tumors in the offspring generally have found no increase in 
risk but most have mainly relied on retrospective exposure assessment. We 
conducted a prospective study on a large birth cohort in Sweden.
METHODS: Women giving birth during 1983-1997 were classified as smokers or 
non-smokers based on information ascertained at the first prenatal visit and 
recorded in the Swedish Birth Register. Follow-up of brain tumor incidence among 
offspring through 1997 was achieved by linkage with the Swedish Cancer Register. 
Hazard ratios were estimated using Cox proportional hazard regression, adjusting 
for demographic characteristics available in the Birth Register.
RESULTS: Brain tumors (n=480) occurred at a rate of 4.5 cases per 100,000 
person-years. Children of women who smoked during pregnancy had an increased 
incidence of brain tumors (hazard ratio = 1.24; 95% confidence interval: 
1.01-1.53). The increase in risk was similar for benign and malignant tumors, 
and was most apparent for astrocytoma. The effect of smoking on the occurrence 
of brain tumors was seen most strongly among 2-4 year-old children.
CONCLUSIONS: These results support a role for maternal smoking during pregnancy 
in the etiology of childhood brain tumors. Our findings should be confirmed in 
other prospective studies.