Effects of ambient air pollution exposure on in vitro fertilization (IVF) outcomes

Air pollution is a significant factor influencing human health. Extensive epidemiological studies have reported that the risk of morbidity and mortality from diseases such as cardiovascular conditions and asthma are associated with air pollution exposure levels. Additionally, the effects of air pollution exposure on pregnancy and birth outcomes have drawn widespread attention, as fetal development might be influenced by air pollution exposure during the gestational period, potentially resulting in pregnancy loss and adverse birth outcomes. However, collecting patient data for exposure assessment at small time intervals, such as the exact date of conception are very challenging. Furthermore, air quality data for exposure assessment often rely on fixed monitoring stations, which are limited in number in some regions. In vitro fertilization (IVF) registries contain specific data on each treatment, recording outcomes such as biochemical pregnancy, clinical pregnancy, and live birth. These records can be linked with air pollution data to investigate associations between air pollution exposure during each stage of IVF treatment and the risk of IVF failure. This thesis addresses this knowledge gap by: Modelling air quality using the ADMS-Urban model for populated Scottish cities to simulate air pollution levels for exposure assessment; Conducting a systematic review to investigate the effects of air pollution exposure on IVF outcomes, identifying preliminary results and study limitations; Investigating associations between IVF outcomes and ambient air pollution exposure (using ADMS-Urban modelled data) with IVF registries from the Scottish cohort between 2010 and 2018; Examining the effects of air pollution exposure (using ADMS-Urban modelled data) during IVF treatment on birth outcomes, including low birth weight, preterm birth, and small for gestational age (SGA). I used the ADMS-Urban model to simulate daily mean air quality data for Glasgow, Edinburgh, Dundee, and Aberdeen from 2010 to 2020. The model receptors were set at the postcode centroid coordinates, and it simulated daily mean air quality data for these cities' postcodes. The model's performance was tested by comparing modelled and observed air pollution concentrations, preparing the simulated air quality data for linkage with IVF records. According to the systematic review, the previous studies’ exposure assessments relied on monitoring stations and spatial interpolation, with limited numbers and inconsistently defined exposure windows, making results hard to compare. More studies are necessary to draw definitive conclusions. The linkage between modelled air pollution and IVF records was achieved using the postcode addresses of IVF patients in Scotland. This approach marks the first use of ADMS-Urban modelled data linked with health records in this manner. The results indicate no significant effects of air pollution exposure on IVF treatment outcomes in Scotland, likely due to low pollution levels. For the associations between birth outcomes and air pollution exposure during complete IVF cycles with successful births, I found that exposure during window 3 (14 days after embryo transfer) was significantly associated with a higher risk of adverse birth outcomes. Overall, this thesis has contributed to understanding the associations between air pollution exposure during IVF treatment and both IVF and birth outcomes.