Does air pollution affect female fertility?

Ovarian reserve — a marker of potential female fertility based on the number of resting follicles in the ovary — has been found in a large-scale study to be adversely affected by high levels of air pollution.

That’s according to the Ovarian Reserve and Exposure to Environmental Pollutants (ORExPo) study of hormone measurements taken from more than 1300 Italian women, the results of which were presented at the Annual Meeting of the European Society of Human Reproduction and Embryology (ESHRE) by Professor Antonio La Marca from the University of Modena and Reggio Emilia, Italy.

Behind the study lay emerging evidence that many environmental chemicals, as well as natural and artificial components of everyday diet, have the potential to disturb the physiological role of hormones, interfering with their biosynthesis, signalling or metabolism. The hormone in this case, anti-Müllerian hormone (AMH), is secreted by cells in the ovary and is now recognised as a reliable circulating marker of ovarian reserve.

“The influence of age and smoking on AMH serum levels is now largely accepted, but a clear effect of environmental factors has not been demonstrated so far,” said Prof La Marca, who was first investigator on the study.

The ORExPo study was in effect an analysis of all AMH measurements taken from women living in the Modena area between 2007 and 2017 and assembled in a large database. The analysis was completed with environmental data and a ‘geo-localisation’ estimate based on each patient’s residence. The assessment of environmental exposure considered daily particulate matter (PM) and values of nitrogen dioxide (NO₂) — a polluting gas which gets into the air from burning fuel.

Results from the AMH measurements collected from 1318 women firstly showed — as expected — that serum AMH levels after the age of 25 were inversely and significantly related to the women’s age. However, it was also found that AMH levels were inversely and significantly related to environmental pollutants defined as PM₁₀, PM_2.5 and NO₂ — an association that was age-independent.

These results were determined by dividing the full dataset into quartiles reflecting PM₁₀, PM_2.5 and NO₂ concentrations, and found significantly lower levels of AMH in the fourth quartile than in the lowest quartiles. The lowest concentration of AMH, reflecting ‘severe ovarian reserve reduction’, was measured in subjects who were exposed to levels of PM₁₀, PM_2.5 and NO₂ above 29.5, 22 and 26 mcg/m³ respectively — values well below the upper limits recommended by the EU and local authorities (40, 25 and 40 mcg /m³ respectively).

Severe ovarian reserve reduction, as reflected in a serum AMH concentration below 1 ng/mL, was significantly more frequent in the fourth quartile than in the first three quartiles for PM₁₀ (62% vs 38%) for PM_2.5 and for NO₂. “This means by our calculations,” said Prof La Marca, “exposure to high levels of PM₁₀, PM_2.5 and NO₂ increases the risk of having a severely reduced ovarian reserve by a factor between 2 and 3.”

Prof La Marca acknowledged that age remains the most important determinant of AMH concentration in women, and added that other factors such as smoking, body weight and long-term hormonal contraception are already recognised as having an impact on AMH. Now it appears that environmental pollutants may too have a significant effect in determining circulating levels of AMH.

“Living in an area associated with high levels of air pollutants in our study increased the risk of severely reduced ovarian reserve by a factor of 2 or 3,” he said.

Image credit: ©stock.adobe.com/au/lukyeee_nuttawut

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