Assessing ambient air pollution's effects on birth outcomes: a Scottish IVF cohort study (2010 -2018)

Ambient air pollution exposure during and before the pregnancy could result in adverse birth outcomes. This study uses data from women undergoing in vitro fertilization (IVF) data to investigate the associations between ambient air pollution exposure and adverse birth outcomes.

This study analyses the associations between adverse birth outcomes, namely low birth weight (LBW), small for gestational age (SGA), and preterm birth and daily mean air pollution exposure during each of four IVF windows. The air pollutants considered were particulate matter with an aerodynamic diameter of less than 10 µm (PM₁₀) and 2.5 µm (PM_2.5), as well as nitrogen dioxide (NO₂), which were estimated using the Atmospheric Dispersion Modelling System (ADMS-Urban). This data was linked to the IVF patients' postcode providing estimates of exposure to air pollutants. Logistic regression models were used to quantify the associations between air pollution exposure and adverse birth outcomes, and conditioning confounding factors. A subgroup analysis was conducted to investigate the differences in the effects of ambient air pollution exposure on the ICSI and IVF groups.

From January 2010 to May 2018, there are 2069 babies were able to be included in this study. We found no significant associations between air pollution exposure and the risk of adverse birth outcomes during window 1(85 days before oocyte retrieval) and 2 (14 days after gonadotrophin medication). With 1 µg⋅m^-3 increase in PM₁₀ concentration during window 3 (14 days after embryo transfer) and 4 (embryo transfer to delivery) led to a 5% (95% CI: 1.05-1.06) and 10% (95% CI: 1.01-1.21) increase in the odds of preterm birth, but not other outcomes. In window 3, every 1 µg⋅m^-3 increase in NO₂ concentrations resulted in a 2% (95% CI: 1.00 - 1.04) increase in the odds of LBW and a 3% (95% CI: 1.00 -1.05) increase in the odds of SGA but showed no effect for preterm birth. The results of the subgroup analysis suggest that the air pollution exposure may have a greater impact on the IVF group compared to the ICSI group.

The results suggest that exposure to air pollution during the very early stage of pregnancy (14 days after conception) may represent the most critical window of susceptibility to an increased risk of adverse birth outcomes.