One of the many things that affects a woman’s ability to conceive and have a healthy pregnancy is environment, but what’s not as clear is exactly which elements influence fertility.
However, one more step toward the answer will be made this week at the annual meeting of the European Society of Human Reproduction and Embryology in Vienna, Austria.
Air Pollution Can Affect AMH
A team of scientists will present a study Wednesday demonstrating that air pollution, like particulate matter and nitrogen dioxide, can affect levels of a hormone called anti-Müllerian hormone, or AMH.
AMH is secreted by follicles in the ovary known as granulosa cells, and doctors can estimate a woman’s ovarian reserve — or how many eggs she has — by measuring levels of AMH.
While some studies show that age and AMH levels can be predictors of ovarian reserve, that assertion has been debated. A low ovarian reserve doesn’t mean that natural conception will be difficult, but it can suggest a woman will have a reduced reproductive lifespan and earlier menopause.
This study used blood samples from 1,318 women living in the northern Italian province of Modena and were used to measure AMH levels. Scientists then measured the environmental pollutants in the residential areas surrounding the women’s addresses, specifically focusing on pollution particles known as PM2.5 and PM10, as well as nitrogen dioxide.
(PM2.5 refers to atmospheric particulate matter that has a diameter of fewer than 2.5 micrometers — about 3 percent the diameter of a human hair — while PM10 describes inhalable particles with diameters 10 micrometers and smaller.)
AMH levels in blood naturally fall with age after a woman is 25. However, once the team took age into account, they still found that AMH levels were lower among the women who lived in more polluted areas.
The women who lived in the most polluted places were two to three times more likely than the others to have AMH levels below 1 nanogram per milliliter. The authors note that this is a severely low ovarian reserve.
The women with the lowest concentration of AMH were exposed to levels of PM10, PM2.5, and nitrous dioxide above 29.5, 22, and 26 mcg/m3 respectively. Yet, these values are below the upper limits considered by the European Union to still be safe.
Audrey Gaskins, Sc.D., is an assistant professor of epidemiology at Emory University. Gaskins is unaffiliated with this study, but she and colleagues recently published a paper in the journal Epidemiology on a similar topic. Instead of measuring AMH as a marker of ovarian reserve, they focused on antral follicle count, which is considered a comparable measurement.
“It is reassuring to see that the Italian researchers are uncovering similar findings to ours that higher exposure to fine particulate air pollution is associated with a lower ovarian reserve and it seems to be a robust effect independent of age,” Gaskins tells Inverse.
But she notes that there are some limitations. For example, while the study accounts for age, it does not factor in the socioeconomic and demographic factors that correlate with air pollution exposure and AMH levels. It also does not appear to control for potential time trends or seasonal effects, which could explain some of the associations.
As a comparison, her study found that among 632 women attending the Massachusetts General Hospital Fertility Center, higher PM2.5 exposure was associated with lower ovarian reserve. Here lower antral follicle count was adjusted for age, BMI, smoking status, as well as the year and season in which the count was measured. But like the Italian team, Gaskin and colleagues also conclude that there’s reason for concern.
“Taken together,” Gaskin says, “the evidence suggests that exposure to relatively low concentrations of air pollution, particularly PM2.5, may decrease human fertility by accelerating ovarian aging in women.”
So what can women do take precautions against accelerating ovarian again? Pressuring governments to take action to reduce unhealthy ozone and fine particle pollution is one way (the U.S. ranks just eighth in the world for cleanest air for particle pollution, and its getting worst). But there’s smaller steps that can be taken as well, like controlling pollution at home with window seals and limited indoor sources of pollution like wood-burning fires.
Background: Many chemicals present within the environment, as well as natural and artificial components of our diet, have the potential to interfere with the physiological role of hormones, interfering with hormone biosynthesis, signalling or metabolism. In the last years AMH, a protein secreted by granulosa cells, has emerged as a reliable marker of ovarian reserve. It is largely accepted the influence of age and smoking on AMH serum levels, although a clear effect of environment has not been demonstrated.
Methods: A longitudinal, observational, retrospective, real-world big data trial was performed. All laboratory AMH measurements of women living in the area surrounding the city of Modena performed from January 2007 to October 2017 at the Central Laboratory of Modena Hospital were extracted and collected in a large database. AMH serum levels were measured with commercial assay (Beckman Coulter). A computing data warehouse was created, in which AMH data were connected to patients’ age and residential address. The database was completed, including environmental data and considering the city where each patient lived for geo-localization. The environmental exposure considered daily particulate matter (PM) and NO2 values.
Results: 1,463 AMH measurements were collected for 1,318 women (mean 1.94 ng/ml, and median of 0.90 ng/ml). AMH was inversely related to patients’ age (Rho=−0.437, P<0.001), although not related to age in patients younger than 25 years (Adjusted R-squared 0.068 P=0.055). On the contrary, AMH was inversely related to age after 25 years of age (Adjusted R-squared 0.120, P<0.001). AMH was inversely related to environmental pollutants, such as PM10 (Rho=−0.088, P=0.001), PM2.5 (Rho=−0.062, P=0.021) and NO2 (Rho=−0.111, P<0.001). This association was age–independent. No relationships were found between AMH and environmental temperatures.