Individual and joint effects of prenatal green spaces, PM and PM exposure on BMI Z-score of children aged two years: A birth cohort study.

Background: Few studies examined the association of prenatal exposure to green spaces with children's body mass index (BMI) Z-score, and no study evaluated the joint effect of prenatal green spaces and PM or PM exposure on children's BMI Z-score. We aimed to assess the individual and joint effects of prenatal green spaces, PM, and PM exposure on BMI Z-score of children aged two years.

Methods: The study was based on a birth cohort in Beijing, China, in which 13,253 mothers (LMP from 2014 to 2017) and their children were included. We estimated prenatal green spaces exposure by calculating average normalized difference vegetation index with 500 m buffers (NDVI-500), prenatal PM and PM exposure based on maternal residential addresses. Weight and height of children were measured at 2 years old. We calculated children's BMI Z-score based on the WHO Standards. Generalized linear regression was used to examine the individual and joint effects of prenatal NDVI-500, PM and PM exposure on children's BMI Z-score.

Results: A 0.1 increase in prenatal NDVI-500 exposure, a 10 μg/m decrease in PM, a 10 μg/m decrease in PM were associated with 0.185 [95% confidence interval (95%CI): 0.155, 0.216], 0.034 (95%CI: 0.015, 0.052) and 0.041 (95%CI: 0.020, 0.061) increase of children's BMI Z-score, respectively. Compared with those exposed to low-level NDVI-500 (not greater than median) and high-level PM (greater than median), the BMI Z-score was higher in children whose mother exposed to high-level of NDVI-500 and low-level PM [β:0.172 (95%CI: 0.131, 0.214), P = 0.003]. Compared with those exposed to low-level NDVI-500 and high-level PM, the BMI Z-score was higher in children whose mother exposed to high-level of NDVI-500 and low-level PM [β:0.169 (95%CI: 0.127, 0.210), P<0.001]. In the trimester-specific analysis, NDVI-500 and PM exposure during the second trimester have a consistent individual effect, together with a joint effect, on child growth.

Conclusion: The study suggested the beneficial effect of prenatal exposure to green spaces on child growth and its interaction with PM and PM, especially in the second trimester. The findings call for developing public health policy to improve green infrastructure and control PM and PM concentrations, in order to promote child growth.