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AIR POLLUTION

Ambient air pollution found unrelated to IVF outcomes

Despite conflicting evidence from some studies, a new large-scale study has found no significant correlation between moderate levels of air pollution and outcomes from IVF.

Published 20 September 2019

A cohort study involving more than 250,000 IVF cycles has found no correlation between treatment outcomes and low daily ambient levels of particulate matter and ozone.

A large retrospective study of more than 250,000 fresh IVF cycles in the USA has found no 'clear evidence' of a meaningful association between reproductive outcomes and daily concentrations of particulate matter and ozone.(1) The study, however, which linked via ZIP code 2010–2012 data from the US National ART Surveillance System (NASS) with the CDC's Environmental Public Health Tracking Network for air pollution, did not include particulate matter with an aerodynamic diameter greater than <2.5 μm (PM2.5) or with nitrogen dioxide (NO2) exposure. Two recent studies, one presented at ESHRE's Annual Meeting in Vienna, have each found that acute exposure to high levels of NO2 and PM10 was associated with a reduction in ovarian reserve, lower ovarian response and fewer high-quality embryos.(2,3)

Air quality in IVF labs and particularly in culture conditions has long been recognised as a factor in embryonic development. Indeed, one of the claims for time-lapse culture is that it limits exposure to any unnecessary ambient pollutants. One study from a single clinic, which was able to compare outcomes when carbon filtration was present, unintentionally absent, and later restored in its lab, found that the absence of carbon filtration was indeed associated with poor fertilisation and early embryo development in fresh (but not frozen) cycles.(4)

At the broader environmental level, Legro et al studied the air pollution levels found around the homes and IVF clinics of 7403 women undergoing their first IVF cycles.(5) They concluded that the effects of declining air quality on reproductive outcomes after IVF were variable and complex, but that increased NO2 concentrations were consistently associated with lower birth rates. Similar conclusions, using AMH as a marker for ovarian reserve, were reported by Antonio La Marca at this year's ESHRE Annual Meeting.(2) This 'real life' study from Modena, which correlated 1463 AMH measurements collected from 1318 women with local assessment of daily particulate matter and nitrogen dioxide levels, found - as expected - that serum AMH levels after the age of 25 were inversely and significantly related to female age, but also related inversely and significantly to PM10, PM2.5 and NO2 environmental pollutants. 'This means by our calculations,' said La Marca in an ESHRE press release, 'that exposure to high levels of PM10, PM2.5 and NO2 increases the risk of having a severely reduced ovarian reserve by a factor between 2 and 3.'

This latest American study - in a retrospective cohort of 250,000 fresh cycles - analysed the effect of daily PM2.5 and ozone concentrations during three time periods of an IVF cycle: cycle start to oocyte retrieval, oocyte retrieval to embryo transfer, and embryo transfer + 14 days. Multivariable logistic regression models were used to estimate adjusted risk ratios, but these showed no 'meaningful' correlation at any of the time phases between reproductive outcomes and average daily concentrations of PM2.5 and only a weak association (implantation and live birth) with ozone levels.

This was, however, a large and complicated study with only two pollutants specifically assessed, and the authors concede that 'given the array of pollutants to which women may be exposed and the complex temporal and spatial interactions between pollutants, it is difficult to assess the role of individual exposures'. Nevertheless, ambient air pollutants have been implicated in higher risks of cardiovascular and other chronic diseases, and it seems possible from IVF laboratory and other population studies that there is indeed a link with fertility, notably with particulate matter of a higher aerodynamic diameter and NO2. As the authors of this report state, more studies are needed.

1. Boulet SL, Zhou Y, Shriber J, et al. Ambient air pollution and in vitro fertilization treatment outcomes. Hum Reprod 2019; doi.org/10.1093/humrep/dez128.

2. La Marca A. Ovarian reserve and exposure to environmental pollutants (ORExPo study). ESHRE Annual Meeting 2019, Abstract 0-204.

3. Carre J, Gatimel N, Moreau J, et al. Influence of air quality on the results of in vitro fertilization attempts: a retrospective study. Eur J Obstet Gynecol Reprod Biol 2017; 210: 116–122.

4. Munch EM, Sparks AE, Duran HE, et al. Lack of carbon air filtration impacts early embryo development. J Assist Reprod Genet 2015; 32: 1009–1017.

5. Legro RS, Sauer MV, Mottla GL, et al. Effect of air quality on assisted human reproduction. Hum Reprod 2010; 25: 1317–1324.