A new study has discovered that living in an area with high concentrations of air pollution can increase the risk of infertility.
The analysis looked at 18,000 couples in China living in locations with varying levels of pollution to determine how it affected their chances of conceiving a child.
It was discovered that couples living in areas with moderately higher concentrations of small particle pollution had a 20 per cent greater risk of infertility - defined by the study as those who did not become pregnant within a year of trying.
Small particle pollution comes from a number of sources, including industrial facilities, smoke from fires and car emissions. It's more dangerous than the larger particles that come from activity like construction work, because small particles can penetrate the deep parts of lungs and sometimes enter the blood.
Researchers could not determine from the study how exactly air pollution damages fertility, though it is known that pollution particles can cause internal inflammation, possibly impacting sperm and egg production.
A recent study of women attending a fertility clinic in the US found that women from areas with higher levels of air pollution often had a lower number of maturing eggs in their ovaries.
Dirty air is also known to affect other aspects of human reproduction, including low birth weights, premature births and miscarriage.
'The results are concerning '
Qin Li, at the Centre for Reproductive Medicine at Peking University Third hospital in China, who led the infertility research, told the Guardian that the results are worrying for prospective parents.
“Numerous studies have noted that air pollution is associated with lots of adverse pregnancy events,” he said.
“Approximately 30% of infertile couples have unexplained infertility... [Our study] indicates that small-particle pollution could be an unignorable risk factor for infertility", Li and colleagues wrote in the study, published in the journal Environment International.
The study revealed that women exposed to small particle pollution which was 10 micrograms per cubic metre higher than others experienced over the course of a year had a 20 per cent higher risk of infertility.
In the study, Chinese couples were exposed to an average pollution level of 57µg/m3. This compares to an average of 13µg/m3 in London.
Tom Clemens, at the University of Edinburgh, UK, commented on the findings, saying that even for areas with lower pollution levels, such as the UK, the results are concerning.
“The size of the effects they observe seem pretty high, which would be concerning if borne out in future studies as well, particularly in low pollution environments," he explained.