In longitudinal cohort studies, the relationships between prenatal and postnatal tobacco smoke exposure and infant wheezing illnesses were compared in two geographically defined populations in Avon, UK and Brno and Znojmo in the South Moravian Region of the Czech Republic.

Pregnant females living in defined regions and with expected dates of delivery between defined dates were recruited. Females completed self-report questionnaires during pregnancy and when their infant was 6 months old. For this analysis, responses to questions about smoking during pregnancy, environmental tobacco smoke (ETS) exposure and reported wheezing illnesses of infants at 6 months after birth were used. Odds ratios for wheeze in relation to the smoking variables were calculated with adjustment for potential confounding effects.

The prevalence of smoking during pregnancy was higher in Avon (17.5%) than the Czech Republic (7.1%). Exposure of infants to ETS during the first 6 months after birth was also reported to be higher in Avon (35.5%) than the Czech Republic (9.7%). The prevalence of reported wheezing by 6 months of age was 21.4% in Avon and 10.3% in Brno and Znojmo. In Avon, there was a significant relationship between infant wheeze and maternal smoking during pregnancy (odds ratio (95% confidence interval) 1.30 (1.09–1.56), p=0.004) but not with environmental exposure after birth (1.11 (0.98–1.25)). In contrast, in Brno and Znojmo in the Czech Republic, there was a significant relationship between infant wheeze and ETS exposure (1.66 (1.17–2.36), p=0.04) but not with maternal smoking during pregnancy (0.99 (0.64–1.55)).

This study demonstrated an apparent difference in the associations between prenatal and postnatal tobacco smoke exposure and infant wheezing illnesses in two populations with different smoking prevalence. The relationships were independent of a number of potential confounding variables that have been associated with infant wheezing. Possible explanations of these observations include dose-related effects of prenatal and postnatal tobacco smoke exposure of infants.