Air pollution detrimental to IVF success

A study presented at ESHRE 2024 shows that increased exposure to fine particulate matter (PM_2.5 and PM₁₀) air pollution prior to oocyte collection (OPU) or frozen embryo transfer (FET) during in vitro fertilization (IVF) is associated with a reduction in live birth rates (LBRs) in subsequent FETs.

“Overall, air quality was excellent, with pollutant levels within published safe limits on >99 percent of days during the study period,” noted study lead investigator Dr Sebastian Leathersich from Dexeus Fertility, Hospital Universitari Dexeus, Barcelona, Spain.

But even in a setting where air quality is exceptional – when the PM_2.5 and PM₁₀ exposures are within the so-called ‘safe’ ranges – he noted that the results still revealed “a strong negative linear association between PM exposure during the 2 weeks and 3 months prior to OPU and subsequent LBRs from those oocytes. This association is independent of the air quality at the time of FET.”

“[The results thus imply that] there does not appear to be a ‘safe’ level of pollution exposure when it comes to human reproduction,” Leathersich stressed.

In the 2 weeks prior to OPU, increasing PM₁₀ exposure was significantly associated with a reduced odds of live birth (p linear trend=0.009), dropping by 38 percent when PM₁₀ concentrations were in the highest quartile compared with the lowest quartile (odds ratio [OR], 0.62).

In the 3 months prior to OPU, increasing PM_2.5 exposure was also tied to a significant reduction in the odds of live birth (p linear trend=0.011). ORs were 0.90 and 0.81 in the respective second and third quartiles, dropping to 0.66 during the fourth quartile. [ESHRE 2024, abstract O-075]

“[These results suggest] that it is the environmental exposures during the periods of oogenesis and follicular development that can have a negative impact on subsequent LBRs,” said Leathersich.

The team retrospectively evaluated 3,657 FETs from 1,835 patients over an 8-year period in a single centre in Perth, Western Australia. The median age was 34.2 years at the time of OPU and 36.1 years at the time of FET. About 48 percent of participants had IVF; the remainder had intracytoplasmic sperm injection. The team assessed air pollutant concentrations over four exposure periods prior to OPU: 24 hours, 2 weeks, 4 weeks, and 3 months.

“This is the first study that has used FET cycles to separately analyse the effects of pollutant exposure during the development of eggs and around the time of ET and early pregnancy. We [were able to] evaluate whether pollution was having an effect on the eggs themselves, or on the early stages of pregnancy,” Leathersich shared in the ESHRE news release.

“[Our] findings suggest that pollution negatively affects the quality of the eggs, not just during the early stages of pregnancy, which is a distinction that has not been previously reported,” he added.

Public health priority

Ambient air pollution is one of the greatest environmental health risks and is estimated to cause over 4M premature deaths annually on a global scale. [https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health, accessed July 16, 2024]

In the news release, Leathersich swerved the spotlight on the global pollution problem. “Climate change and pollution remain the greatest threats to human health, and human reproduction is not immune to this.”

“Even in a part of the world with exceptional air quality, where very few days exceed the internationally accepted upper limits for pollution, there is a strong negative correlation between the amount of air pollution and the LBR in FET cycles. Minimizing pollutant exposure must be a key public health priority,” he stressed.

ESHRE Chair-Elect Professor Dr Anis Feki echoed Leathersich’s sentiments. “This important study highlights a significant link between air pollution and lower IVF success rates, with a notable reduction in live births associated with higher PM exposure before oocyte retrieval. These findings emphasize the need for ongoing attention to environmental factors in reproductive health.”