Exposure to fine particulate matter, a common air pollutant, can significantly decrease the odds of a successful in vitro fertilization (IVF) cycle, even in areas with good air quality, a new study found.

The Australian study published Sunday in the European Society of Human Reproduction and Embryology found that exposure to pollution before the retrieval of eggs during IVF can reduce the odds of achieving a live birth by almost 40 per cent.

“Climate change and pollution remain the greatest threats to human health, and human reproduction is not immune to this,” said Dr. Sebastian Leathersich, lead author of the study and a fertility specialist based in Australia.

“We found that increased exposure to particulate matter pollution (PM2.5 and PM10) in the weeks and months before egg collection were associated with reduced live birth rates, regardless of the pollution levels at the time of the embryo transfer,” he told Global News in an email sent Thursday.

Outdoor air pollution is one of the greatest environmental risks to health and is estimated to cause over four million premature deaths per year worldwide, a 2022 World Health Organization (WHO) report found.

Exposure to fine particulate matter is associated with a range of adverse health conditions, including cardiovascular and respiratory diseases and cancer, the WHO reported.

Health Canada estimates that air pollution contributes to 15,300 premature deaths annually in Canada, with many more people losing days suffering from asthma and acute respiratory symptoms as a result of pollution.

When it comes to air pollution and IVF, the researchers said little has been studied.

“This is the first study to look specifically at frozen embryo transfers, accounting for the conditions at the time of egg collection and those at the time of embryo transfer,” Leathersich said.

“Given more and more women having IVF are using frozen embryo transfers, where the embryos can be used months or years after the eggs are collected, we wanted to look at whether the pollution levels around the time of egg collection or around the time of embryo transfer were more important.”

This eight-year study in Perth, Australia, looked at more than 3,600 frozen embryo transfers involving 1,836 females. The average age of the patient was 34.5 years old when the eggs were collected and 36.1 years old when the embryo transfer happened.

The researchers examined air pollution levels during four timeframes before egg collection (24 hours, two weeks, four weeks and three months).

The study found that patients exposed to the highest levels of air pollution in the two weeks before egg collection had a 38 per cent lower chance of having a live birth compared with those with the lowest levels of exposure.

The researchers also found that patients exposed to higher levels of air pollution in the three months leading up to egg retrieval had a lower chance of having a live birth.

The negative impact of air pollution was also seen despite excellent overall air quality during the study period, with particulate matter levels exceeding WHO guidelines on just 0.4 per cent and 4.5 per cent of the study days, respectively.

The WHO’s guidelines recommend an annual average concentration of PM2.5 of five micrograms per cubic metre of air. PM2.5 refers to airborne particles so tiny that they can penetrate the lungs when you breathe and enter the bloodstream.

“This association is independent of the air quality at the time of frozen embryo transfer. 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,” Leathersich said.

Jamie Seabrook, a professor in the Department of Epidemiology and Biostatistics at Western University in London, Ont., described the study as a crucial contribution to the understanding of how maternal health is impacted by pollution.

In 2019, Seabrook helped publish a study in Environmental Research examining the effects of pollution on pregnancy. The study revealed that women experiencing typical high exposure to sulphur dioxide were 30 per cent more likely to have a low birth weight baby and 20 per cent more likely to deliver prematurely, compared with those with typical low exposure levels.

“I would say that evidence is accumulating in this area,” Seabrook said, emphasizing the critical importance of such research as air quality increasingly impacts human health.

In Seabrooke’s study, researchers found that pollutants enter the lungs of pregnant people and subsequently travel to the placenta. This means that increased exposure to these pollutants results in them passing through the mother’s lungs and reaching the fetus.

When discussing how pollution affects the IVF process, Leathersich told Global News that it’s still unclear how exposure impacts the outcomes. The study focuses on establishing connections rather than exploring the underlying mechanics, he added.

However, he said that particulate matter is known to increase inflammation, cause cell and DNA damage and increase oxidative stress.

“Studies in the last few years have actually found pollution particles within human ovaries and developing follicles, showing us that the pollution we are exposed to can make its way directly into the ovaries,” he said.

“We are planning to evaluate this further over the next few years, with studies planned that will look directly at the impacts of pollution exposure on human eggs.”

While complete avoidance of pollutants might not be possible, Leathersich offered some tips for those who are pregnant or undergoing IVF to minimize their exposure.

“This could include staying inside on high-pollution days (or) using air filters. However, ultimately, reproductive health is part of the larger picture when it comes to pollution, and strong government and industry action is urgently required to reduce emissions and improve health outcomes,” he said.

Seabrook echoed these sentiments and emphasized the importance of keeping car windows up during rush hour traffic.

“During rush hour you should always be driving with the windows up … as you are breathing in that air during rush hour when pollution levels are more spiked. So if you are pregnant or trying to become pregnant, it’s really important during rush hour (to close your windows).”