The effect window for sulfur dioxide exposure in pregnancy on childhood asthma and wheezing: A case-control study.

BACKGROUND The relationship between prenatal exposure to sulfur dioxide (SO2) and childhood wheezing and asthma is unclear. OBJECTIVE To explore the association between prenatal exposure to SO2 and childhood wheeze and asthma. To investigate the effects for the exposure during different pregnancy trimesters. METHODS We conducted a cross-sectional study firstly in Jinan City to get the prevalence of wheeze and asthma on children aged 18 months to 3 years. And then, we designed a case-control study based on population to evaluate the association between prenatal SO2 exposure and childhood asthma and wheezing. Based on the starting and ending date of pregnancy and specific residential addresses, the individual concentrations of SO2 during pregnancy was evaluated using an inverse distance weighted model. RESULTS The prevalence of wheeze and asthma on children aged 18 months to 3 years was 2.07% in our cross-sectional study. 236 cases and 1445 controls were available for exposure estimates. The OR (95% CI) of 1.296 (1.130-1.491) was significant after adjusting for the covariates. In the first and third trimesters, the effects were enhanced to 1.602 (1.275-2.022) and 1.448 (1.179-1.783) in the multi-pollutant model with adjusting the effects of other trimesters. Coincidentally, the SO2 exposure level of the case in the first trimester was higher than that in the second and third trimesters (P < 0.001); however, there was no significant difference in exposure levels of the case between the second and third trimesters of pregnancy (P = 0.381). CONCLUSION Prenatal exposure to higher concentration of SO2 could increase the risk of asthma and wheezing in younger children. The first trimester might be just the window for the toxic effect, while the third trimester was the sensitive window for the effect of SO2 exposure during pregnancy on childhood asthma.