High pollution levels can increase the risk of infertility by up to 20 percent, a study in China has found.

The researchers wrote that their findings point to pollution as 'an unignorable risk factor for infertility'. It is believed to be the first study that examines the link between air pollution and infertility in the general population, rather than solely in fertility patients.

'Numerous studies have noted that air pollution is associated with lots of adverse pregnancy events,' lead author Dr Qin Li, from the Centre for Reproductive Medicine at Peking University Third Hospital in Beijing, China, told the Guardian. 'Our study samples were recruited from the general population, so our findings may be more generalisable,' he added.

The study, published in the journal Environmental International, analysed 10,211 couples across eight Chinese provinces. The participants were recruited from the China Fertility Survey of Married Women, a national database of couples trying to conceive. The study focused on small, particulate air pollution, called PM2.5, most commonly produced by cars and industry. Infertility was defined as the failure to become pregnant after one year or more of attempting to conceive.

The researchers estimated each participant's PM2.5 exposure over one, three, and five years. After accounting for factors such as age and lifestyle, they found that for every ten microgram increase in PM2.5 exposure, the risk of infertility rose by 20 percent. The average exposure level for each participant was 57 micrograms per metre cubed - much higher than the UK average, which varies between ten and 15 micrograms. Furthermore, when comparing the quarter of women exposed to the lowest amounts of pollution to the quarter exposed to the highest, infertility rates jumped from 15 to 26 percent.

The researchers wrote that with further research, their findings 'might explain the increased infertility rates in polluted areas.' Currently, 30 percent of infertility remains unexplained following medical tests.

This is not the first time low air quality has been associated with poor reproductive health. PM2.5 has been linked to circulatory and inflammatory health problems, as well as low quality sperm production. A recent study of 600 fertility patients in the US also showed increased pollution exposure was associated with a lower number of maturing eggs in patients' ovaries.

Dr Tom Clemens, an expert in health and environment at the University of Edinburgh, remarked that the findings 'would be concerning if borne out in future studies as well, particularly in low pollution environments.' Commenting on how the risk of infertility from air pollution could be mitigated, Dr Clemens added: 'The emphasis should lie with policymakers, not with individuals.'

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Reproduced from BioNews with permission, a web- and email-based source of news, information and comment on assisted reproduction and human genetics, published by Progress Educational Trust.