Periconception Exposure to Air Pollution and Birth Outcomes

Abstract

Healthy gamete formation, spermatogenesis and oogenesis, and fetal development are essential for a successful pregnancy, and there is evidence that exposure to ambient air pollution including nitrogen dioxide and particulate matter during this period may affect fertility and/or birth outcomes. Previous studies did not consider individual exposure, including time-activity patterns and indoor air exposure but personal exposure monitoring tools are increasingly available and can help to overcome this issue. This thesis seeks to determine whether periconception exposure to ambient air pollution could influence sperm quality, fertility, and birth outcomes. In addition, feasibility studies were undertaken to assess the suitability of one personal exposure monitor to assess air pollution exposure and the practicality of recruiting couples (women and men) who attempt to conceive through ART treatment, and of collecting data on personal exposure to air pollutants and other contributing factors. Two retrospective studies were conducted using data from (i) a case-referent (CHAPS-UK) study on 1,681 men seeking fertility diagnosis at various UK fertility centers between 1999 and 2002, and (ii) a cross- sectional study of 1,541 of women who underwent a first fresh ART treatment cycle in Greater Manchester at Old St. Mary’s Hospital between 2015 and 2019. Exposures to PM10 and NO2 were estimated using land use regression models, and then calculated across different time frames related to sperm quality, fertility and birth outcomes. A variety of statistical models were utilized for the analysis depending on the outcome of interest, including a multivariate linear and logistic regression, and a linear and logistic mixed- effect model, with confounding factors taken into account. The overall findings indicate that periconception ambient air pollution did not significantly influence most sperm parameters, fertility outcomes, or birth outcomes. However, the findings suggest that NO2 air pollution levels in urban areas may significantly affect sperm morphology within the studied UK population. The majority of the measurements from the personal monitoring tool "Plume Lab Flow2" show a weak correlation coefficient (r < 0.4) with the reference instruments at various field locations (indoor, road site, and outdoors). The feasibility study findings provide another prospective, showing a low recruitment rate (only 10% of the initial participants were successfully recruited), suggesting potential feasibility challenges for future studies that are conducted prospectively. The feasibility study also found varying levels of air pollutants and chemical hazards across participants and by gender, despite similar demographic characteristics, possibly due to differences in activity patterns. In conclusion, the relevance of sperm morphology in fertility makes these findings significant for public health interventions. Furthermore, this study provides researchers and fertility care centres with comprehensive understanding of the recruitment process, suggesting that reproductive health awareness and knowledge may increase participation rates in future studies.