User:C.Preston20/sandbox

Women
In women undergoing IVF treatment, increases in NO2 both at the patient’s address and by the IVF lab were significantly associated with a lower live birth rate.

In the general population, there is a significant increase in miscarriage rate in women exposed to NO2 compared to the non-exposed group.

Women
CO exposure is significantly associated with stillbirth in the second and third trimester.

Polycystic aromatic hydrocarbons
Polycystic aromatic hydrocarbons (PAHs) have been associated with reduced fertility. Benzo(a)pyrene (BaP) is a well-known PAH and carcinogen which is often found in exhaust fumes and cigarette smoke (Canipari et al, 2020). PAHs have been reported to administer their toxic effects through oxidative stress by increasing the production of Reactive Oxygen Species (ROS) which can result in inflammation and cell death. More long-term exposure to PAHs can result in DNA damage and reduced repair (da Silva Junior et al, 2021).

Men
Exposure to BaP has been reported to reduce sperm motility and increasing the exposure worsens this effect. Research has demonstrated that more BaPs were found in men with reported fertility issues compared to men without (Plunk and Richards, 2020).

Women
Studies have also shown that BaPs can affect folliculogenesis and ovarian development by reducing the number of ovarian germ cells via triggering cell death pathways and inducing inflammation which can lead to ovarian damage (Perono et al, 2022).

Particulate Matter
Particulate matter (PM) refers to the collection of solids and liquids suspended in the air. These can be harmful to humans when exposed to in day to day life, and more research has shown that these effects may be more extensive than first thought; particularly on male fertility. Within the spectrum of PM there are different weights, such as PM2.5 which are tiny particles of 2.5 microns in width or smaller, compared with PM10 which are classified as 10 microns in diameter or less.

Men
In a study based in California it was found that as exposure to PM2.5 increased sperm motility decreased and morphology became more abnormal. Similarly, in Poland exposure to PM2.5 and PM10 lead to an increase in the percentage of cells with immature chromatin (DNA that has not fully developed or has developed abnormally).

In Turkey, a study looked at the fertility of men who work as toll collectors and are therefore exposed to high levels of traffic pollutants daily. Traffic pollution often has high levels of PM10 alongside carbon monoxide and nitrous oxides. In this study group there were significant differences in sperm count and motility when compared to a control group with limited air pollution exposure. However, it is important to note that there are studies where limited effects on male fertility were found, and therefore more research is needed in this field to fully understand the effects of air pollution on fertility.

Women
In women, whilst overall effects on fertility did not seem significant there was an association was found between increased exposure to PM10 and early miscarriage. Exposure to smaller particulate matter, PM2.5, was seen to have an effect on conception rates in women undergoing IVF but not with live birth rates.

Ground-level ozone pollution[edit]
Ground-level ozone (O3), when in high concentrations, is regarded as an air pollutant and is often found in smog in industrial areas. O3 is largely produced by chemical reactions involving NOx gases (nitrous oxides, especially from combustion) and volatile organic compounds in the presence of sunlight.

There is limited research pertaining to the effect that ozone pollution does have on fertility (Conforti et al 2018). At present, there is no evidence to suggest that ozone exposure poses a deleterious effect on spontaneous fertility in either females or males. However, there have been studies which suggest that high levels of ozone pollution (often a problem in the summer months) do exert an effect on in vitro fertilisation (IVF) outcomes. In fact, within an IVF population, NOx and ozone pollutants were linked with reduced rates of live birth (Conforti et al 2018).

Furthermore, whilst most research on this topic is focused on the direct human exposure of air pollution, other studies have analysed the impact of air pollution on gametes and embryos within IVF laboratories. Multiple studies have reported a marked improvement in embryo quality, implantation and pregnancy rates after IVF laboratories have implemented air filters in a concerted effort to reduce levels of air pollution (Frutos et al 2014). Therefore, ozone pollution is considered to have a negative impact on the success of assisted reproductive technologies (ART) when occurring at high levels.

However, ozone is thought to act in a biphasic manner where a positive effect on live birth is observed when ozone exposure is limited to before IVF embryo implantation (Checa Vizcaíno, Miguel A., Mireia González-Comadran, and Benedicte Jacquemin. “Outdoor Air Pollution and Human Infertility: a Systematic Review.” Fertility and sterility 106.4 (2016): 897–904.e1. Web). Conversely, a negative effect is demonstrated upon exposure to ozone after embryo implantation (Carré et al 2017).

In addition to this, retrospective and prospective studies evaluating the effect of several traffic pollutants (of which ground-level ozone is one) highlighted a significant decrease in live birth rates and miscarriages (Frutos et al 2014).

In terms of male fertility, ozone is reported to cause a significant decrease in sperm concentration measured in semen after exposure ( https://rdcu.be/cWWgF ). Similarly, sperm vitality (the proportion of alive spermatozoa in a sample) was demonstrated to be diminished in a handful of studies (Carré et al 2017). This demonstrates that ozone air pollution exhibits a significantly negative effect of air pollution on this parameter. However, findings on the effect of ozone exposure on male fertility are somewhat discordant, highlighting the need for further research (Carré et al 2017).