Residential greenness and pollen exposure across gestational trimesters in relation to preschool wheezing: Results for the PIPO birth cohort

Introduction: Previous studies on prenatal green space exposure and early respiratory health show inconsistent results. This may reflect stage-specific in utero effects and pollen influence. We examine associations of surrounding greenness and pollen exposure during pregnancy (overall and by trimester) with preschool wheezing, and assess potential mediation by pollen.

Methods: We used data from the PIPO birth cohort (n = 860). Wheezing was reported biannually between 18 and 48 months of age. Residential greenness was measured with Normalized Difference Vegetation Index (NDVI) in 100 and 250 m buffer. Cumulative grass and birch pollen was estimated using modelled airborne pollen counts and categorized per trimester into no, low and high. All exposures were assessed for the overall pregnancy and per trimester. We used Generalized Estimated Equations to obtain odds ratios (OR) and 95% confidence intervals (CI). To assess mediation by pollen we used a data duplication algorithm with a generalized estimation approach.

Results: Approximately 10% of participants wheezed. During pregnancy, greenness (OR = 1.07, CI: 1.05-1.08) and grass pollen exposure (OR = 1.09, CI: 1.03-1.15) increased the odds of wheezing, while birch pollen decreased it (OR = 0.86, CI:0.87-1.00). Per trimester, more greenness during the 2nd trimester increased the odds (OR = 1.21, CI: 1.16-1.26), whereas third-trimester greenness decreased it (OR = 0.87, CI: 0.84-0.91). Grass pollen exposure in the 1st and 3rd trimesters increased the odds of wheezing (OR = 1.23, CI: 1.12-1.34 and OR = 1.13, CI: 1.00-1.27, respectively), while birch pollen exposure in the 1st and 2nd trimesters decreased the odds (OR = 0.88, CI: 0.77-1.00 and OR = 0.83, CI: 0.73-0.95, respectively). No significant associations were found for greenness in the 1st trimester, grass pollen in the 2nd trimester, and birch pollen in the 1st and 3rd trimester. Mediation analysis showed large uncertainty.

Discussion: Surrounding greenness and pollen exposure during pregnancy may impact the likelihood of preschool wheezing differently depending on the timing of exposure and the pollen type.