A recent large-scale study has indicated that high levels of air pollution could reduce the chance of pregnancy following fertility treatment.
Women exposed to increased concentrations of nitrogen dioxide, carbon monoxide and ambient particulate matter had a lower rate of conception following fertility treatment and a higher chance of early pregnancy loss compared with women exposed to lower concentrations of these pollutants.
Researchers at the CHA University School of Medicine in Seoul, South Korea, investigated whether the concentration of five common air pollutants affected the outcome of over 6600 treatment cycles performed at the CHA fertility centre between 2006 and 2014. Using data from 40 air-quality monitoring sites across Seoul, the average daily concentrations of nitrogen dioxide, carbon monoxide, sulphur dioxide, ozone and PM10 (particulate matter with a diameter of less than 10µm), were calculated for each city district over the nine-year study period.
Individual exposures were estimated for each participant based on their residential address at the time of their fertility treatment. The investigators analysed pollutant exposure levels for each participant over four different time periods: at the start of controlled ovarian stimulation to oocyte retrieval; oocyte retrieval to embryo transfer; embryo transfer to pregnancy test; and the start of controlled ovarian stimulation to pregnancy test.
Fertility outcomes were not affected by the exposure levels of sulphur dioxide and ozone. In contrast, exposure to increased levels of nitrogen dioxide or carbon monoxide during controlled ovarian stimulation was associated with a reduced chance of conception.
In addition, increased exposure to nitrogen dioxide, carbon monoxide or PM10 following the embryo transfer was associated with a lower chance of treatment success. For those women that did achieve a positive pregnancy test following treatment, increased exposure to nitrogen dioxide or PM10 post-embryo transfer increased the risk of an early pregnancy loss.
While its findings may help to improve understanding of the conception process, it may be of limited practical application for those individuals undergoing fertility treatment. In a conversation with Reuters, Dr Lyndsey Darrow, an environmental epidemiologist at Emory University in Atlanta, Georgia, acknowledged that measures to reduce outdoor air pollution will require considerable public investment.
She said: 'Ultimately there is a limit to how much individuals can control their own air pollution exposures. Outdoor pollution is one of those problems we can only address through collective action.'