Air pollution during fertility treatment affects live birth rate

Exposure to higher levels of particulate matter, in the weeks and months leading up to oocyte retrieval, is linked to lower live birth rate among fertility patients. 

While the link between air pollution and infertility has been understood for a while (see BioNews 1218, 1133, 1119), there is little understanding of the mechanisms that underpin it. A team from Perth carried out a retrospective cohort study over a period of eight years from 2013-2021, in which they analysed the pollution levels women were exposed to in the weeks and months leading up to oocyte retrieval, and then frozen embryo transfer. Researchers presented the non-peer-reviewed results on Monday 8 July 2024 at the 40th annual meeting of the European Society of Human Reproduction and Embryology (ESHRE).

Dr Sebastian Leathersich, lead author of the study, explained: 'This is the first study that has used frozen embryo transfer cycles to separately analyse the effects of pollutant exposure during the development of eggs and around the time of embryo transfer and early pregnancy. We could therefore evaluate whether pollution was having an effect on the eggs themselves, or on the early stages of pregnancy.'

Pregnancy and live birth rates for 1835 patients who underwent 3659 frozen embryo transfers, were compared to data held on daily air pollutant concentrations in the three months and two weeks before women had oocyte retrieval and frozen embryo transfer. 

Researchers discovered that women exposed to the highest quartile of particulate matter in the two weeks before oocyte retrieval experienced a 38 percent lower live birth rate than those exposed to the lowest quartile of particulate matter in the same period. A lower live birth rate was also observed in patients who had been exposed to higher particulate matter in the three months before oocyte retrieval, but levels of particulate matter prior to frozen embryo transfer did not affect live birth rates. 

Pregnancy rates were not significantly affected by exposure to air pollution. Authors note the air quality of the region was good throughout the study period.  

Dr Leathersich said: 'These findings suggest that pollution negatively affects the quality of the eggs, not just the early stages of pregnancy, which is a distinction that has not been previously reported.'

Ephia Yasmin, a consultant and subspecialist in reproductive medicine and surgery at University College London Hospital and secretary of the British Fertility Society who was not involved in the research told BioNews: 'There is a need to replicate the study in other places but does send a strong message of the wide-ranging negative impact of air pollution.'

A separate non-peer-reviewed study presented at the ESHRE conference by researchers in Spain, of which Dr Leathersich is also an author, showed the level of air pollution on the day of frozen embryo transfer can reduce the chance of live birth. 

Researchers looked at the levels of five air pollutants and found that higher levels of carbon monoxide were associated with higher miscarriage and lower live birth rate in people undergoing IVF with frozen embryos.