Discussion
The current analysis of the population-based Espoo Cohort Study aimed to investigate the association between residential green vegetation during pregnancy and early life and the risk of asthma, with a special interest in trimester-specific and seasonal effects. Our study showed that exposure to abundant greenness during pregnancy is associated with an increased risk of asthma in children. Specifically, maternal exposure during pregnancy to residential greenness during the spring season was related to a significantly increased risk of asthma in the offspring. Furthermore, the association was stronger when the mothers had such exposure to greenness in their third trimester in comparison to when exposure was in earlier trimesters.