Seasonal air pollution found to undermine IVF success

Research links winter spikes in PM2.5 air pollution to lower pregnancy and live birth rates in ART patients, raising concerns over fertility impacts of environmental exposure.

Study: Environmental pollution and human fertility: investigating the relationship between PM2.5 exposure and assisted reproductive technology outcomes. Image Credit: Shutterstock AI Generator / Shutterstock.com

A recent study published in BMC Public Health explores the impact of seasonal fluctuations in fine particulate matter (PM) with a diameter of 2.5 µm or less (PM_2.5) pollution on the outcomes of assisted reproductive technology (ART).

How does air pollution impact fertility?

The success of ART procedures can be affected by various factors, some of which include age, lifestyle, and genetics. To date, the impact of PM_2.5 exposure on reproductive health, particularly ART outcomes, remains unclear.

Long-term exposure to PM_2.5 air pollution significantly increases the risk of developing cardiovascular and respiratory diseases. Current evidence suggests that air pollution can also lead to reduced fertility rates and a greater risk of pregnancy complications such as reduced life birth rates. As a result, clinicians will often recommend limiting exposure to air pollution at least three months before initiating in vitro fertilization (IVF) treatment.

Despite these observations, few studies have investigation the impact of ambient PM_2.5 levels on ART outcomes across seasons.

About the study

The current study was conducted at Shangqiu’s First People’s Hospital and included 13,476 patients who were treated for infertility issues with ART between February 2018 and December 2022. There were approximately 4,000 patients each with spring and summer treatments, as compared to 2,300 and 3,400 patients treated during winter and autumn, respectively.

The period during which PM_2.5 levels were considered began at controlled ovarian stimulation and ended within 30 days of the pregnancy test. This period is considered a critical window of success for optimal oocyte and embryo development and implantation, respectively.

Study findings

With comparable gonadotropin use, multiple reproductive outcomes changed during all seasons and correlated with PM_2.5 exposure. These included both early stages in the ART process like the number of oocytes and how many entered metaphase II (MII), the number of embryos suitable for transfer, and the number of good-quality embryos.

After adjusting for age and expected changes in seasonal rates, a significant negative association was observed between PM_2.5 exposure and both pregnancy and life birth rates. PM_2.5 exposure did not significantly affect miscarriage rates.

As compared to winter months, the spring and summer seasons were associated with a greater number of pregnancy rates for each transfer, with this difference statistically significant between winter and spring months. Live birth rates were also higher during the spring, summer, and autumn months.

The findings of this study demonstrate a consistent adverse relationship between PM_2.5 levels and important ART outcomes, including oocyte number, MII oocyte number, transferable embryos, and good-quality embros.”

Dissecting the mechanisms of PM_2.5-mediated reproductive toxicity

Following the inhalation or ingestion of PM_2.5, these particles can enter systemic circulation to reach the embryos and negatively impact optimal oocyte and embryo development. Several studies have reported that PM_2.5 exposure induces the production of reactive oxygen species (ROS), mitochondrial dysfunction, DNA damage, and early apoptosis, all of which can diminish the quality of oocytes and prevent embryo implantation.  

Within the female reproductive system, PM_2.5 exposure can also damage endometrial cells, thereby inducing oxidative stress and inflammation that is not conducive for embryo attachment to the endometrial lining. PM_2.5 exposure may also alter the expression of adhesion molecules, growth factors, and other substrates that are essential for successful embryo implantation.

PM_2.5 exerts toxic effects on oocytes and embryos, directly disrupting cellular processes and ultimately impairing fertility outcomes.”

In addition to the toxic effects of PM_2.5 exposure on maternal reproductive health, various aspects of male fertility can similarly be impacted by PM_2.5. Previously, researchers have reported that PM_2.5 exposure reduces sperm quality and density by targeting the forehead box protein O1 (FOXO1), in addition to reducing testosterone levels and increasing inflammation within the testes.

Conclusions

Taken together, the study findings indicate a seasonal influence on the effects PM_2.5 air pollution on ART outcomes, as live birth rates were significantly lower during the winter months as compared to other seasons of the year. Although the reproductive toxicity associated with PM_2.5 is likely multifactorial, additional studies are needed to elucidate the exact mechanisms by which PM_2.5 interferes with the potential success of ART treatments.