# Pollution and pregnancy

The health of a mother directly affects the fetus during pregnancy. High levels of pollution where pregnant women reside can have adverse health effects on fetuses.
Previous studies have found correlations between exposure to vehicle pollutants and certain diseases such as asthma, lung and heart disease, and cancer among others. Car pollutants include carbon monoxide, nitrogen oxides, particulate matter (fine dusts and soot), and toxic air pollutants While these pollutants affect the general health of populations, they are known to also have specific adverse effects on expectant mothers, their fetuses and children.

## Fertility

Various air pollutants have an effect on fertility. For instance, an increase in NO$_2$ is significantly associated with a lower live birth rate in women undergoing IVF treatment. In the general population, there is a significant increase in miscarriage rate in women exposed to NO$_2$ compared to those not exposed. Similarly, CO exposure is significantly associated with stillbirth in the second and third trimester.

### Polycyclic aromatic hydrocarbons

Polycyclic 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. 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.
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.
Studies have 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.

### Particulate matter

A study in California found that increased exposure to PM$_{2.5}$ led to decreased sperm motility and increased abnormal morphology. Similarly, in Poland exposure to PM$_{2.5}$ and PM$_{10}$ led 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 examined 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 PM$_{10}$ alongside carbon monoxide and nitrogen oxides. There were significant differences in sperm count and motility in this study group compared to a control group with limited air pollution exposure.
In women, while overall effects on fertility do not appear significant there is an association between increased exposure to PM$_{10}$ and early miscarriage. Exposure to smaller particulate matter, PM$_{2.5}$, appears to have an effect on conception rates in women undergoing IVF but does not affect live birth rates.

### Ground-level ozone pollution

There is limited research about the effect that ozone pollution has on fertility. 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, exert an effect on in vitro fertilisation (IVF) outcomes. Within an IVF population, NO$_x$ and ozone pollutants were linked with reduced rates of live birth.
While 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.
In terms of male fertility, ozone is reported to cause a significant decrease in the concentration and count of sperm in semen after exposure. Similarly, sperm vitality, the proportion of live spermatozoa in a sample, was demonstrated to be diminished as a result of exposure to air pollution. However, findings on the effect of ozone exposure on male fertility are somewhat discordant.

## Population characteristics

Areas with high levels of nitrogen dioxide in the air, which is an output of vehicular air pollution, are shown to have negative effects on fetuses. Effects of the exposure include reduced fetal growth, premature birth, and respiratory conditions. Two studies were conducted to evaluate the effects of nitrogen dioxide on fetuses in the southern United States as well as Valencia, Spain. In the United States, babies that were born prematurely were 94% more likely to have been exposed to high levels of pollution than those that were not premature. In Spain, fetuses that were small for gestational age in terms of weight were 37% more likely to have been exposed to high levels of air pollution than those that were not small for gestational age in terms of weight.
In Los Angeles County, researchers found a higher risk in premature birth (10-20%) and low birth weight for infants whose mothers lived near high traffic areas Studies conducted on populations living near the 405 and 710 interstates in Southern California found their exposure to particulate vehicle emissions to be almost 25 times higher than for people living 1000 ft from the freeways. This research also concluded that particulate vehicle emissions are more toxic to children's health than other particles such as Carbon Monoxide and Nitrogen Dioxide

## Dangers of vehicle emissions
### Carbon monoxide

Carbon monoxide (CO) is directly released from motor vehicles engines, which are a major source of this pollutant in the LA Basin 5. CO inhaled by pregnant women may threaten the unborn child's growth and mental development. Because CO competes with Oxygen to achieve dispersion throughout the blood stream, fetal hypoxia (lack of oxygen) may result at high levels of maternal CO exposure, however the exact amount of exposure of CO to become a fetal threat is unknown High levels of carbon monoxide are also found in cigarettes, it is advised that pregnant women avoid smoking so as to not run the risk of affecting their child's growth or mental development. For further information on Carbon Monoxide and its effects on human health please see, Carbon monoxide poisoning.

### Nitrogen oxides

Nitrogen oxides (NO) are common air pollutants found throughout most of the United States. You can be exposed to these oxides by breathing polluted air, which is most commonly found in areas with heavy motor vehicle traffic Exposure to high levels of Nitrogen oxides damages tissues of the throat and upper respiratory tract and can interfere with the body's ability to carry oxygen. High exposure to nitrogen dioxide may cause fetal mutations, damage a developing fetus, and decrease a woman's ability to become pregnant. Studies have also shown that higher exposures to NO inhibit embryo development during both traditional pregnancies and artificial inseminations

### Particulate matter

Examples of particulate matter include ash from smoke in campfires, dust particles around your house, and smoke coming from car exhaust pipes; in areas close to freeways this is a problem. A study conducted on European women indicated that higher exposure to particulate matter during the initial first weeks of their pregnancy resulted in low birth weight babies This toxin is also considered to be the most dangerous of the three because it can be basically anything small enough to be inhaled. This may also be due to the fact that brain growth begins within the first month of conception.

## Low-birth weight (LBW) and preterm delivery

Both household air pollution and ambient air pollution are associated with low birth weight and pre-term delivery. This can lead to fatal outcomes, especially in developing countries.
A previous study conducted in the Los Angeles Basin of Southern California reported a consistent association between levels of CO and particulate matter during the first trimester and the last six weeks prior to birth and risk of preterm birth. Prematurity in babies is accompanied by an array of health complications. Children born prematurely are at highest risk for developing Infant respiratory distress syndrome, gastrointestinal, and hematologic diseases, central nervous system (CNS) problems such as hearing loss, are more prone to infections, and at risk for hearing and vision loss.
Babies born of low weight are also at risk for respiratory, gastrointestinal, cardiac, CNS, infection and vision problems. These gestational issues persist until the adult years for most children and result in high blood pressure, Type II Diabetes, and other heart diseases.
Prematurity and Low Birth Weight caused by air pollution also affects fetal brain development. This is of importance since lack of proper brain development will not allow a child's brain to form proper synapse connections which will negatively affect the child's speech, learning abilities, and social skills.
Exposure to air pollution not only affects newborns in early stages of their development, it can also have lifelong consequences for children exposed from the time of conception to when they reach two years of age. Air pollution has been found to cause lower birth weights, insufficient development of the immune system and organs, and premature births. These birth effects have been linked to respiratory issues that can persist into one's long-term health.

## Long-term and short-term effects on babies

Exposure to vehicle air pollutants has been noted as primary cause for infant mortality and morbidity, and is also argued to be a cause of chronic diseases such as asthma in child and adulthood

### Asthma

The number of children affected by asthma has increased in past decades the point where it is now the most chronic illness in children and the most common cause of children hospitalizations in the U.S. causing it to also be a number one contributor to school absences Excessive school absences ultimately affect the child's learning ability, and decrease their time to socialize with kids their age. It is not uncommon for children who suffer from asthma to oftentimes repeat grades due to failure to keep up academically. If students are not repeating grades they are highly likely to dropout prior to graduation over their non-affected peers.

### Respiratory problems

Studies have found that children who are exposed to higher levels of car pollutants report higher respiratory problems including wheezing, ear and throat infections and have a higher incidence of physician-diagnosed asthma. Bronchiolitis is also found in greater amounts when the child's home is around high amounts of traffic.

### Cancer

Children living in close proximity to high traffic areas are also eight times more likely to develop leukemia compared to children who do not This finding indicates that children who develop cancer as a result of traffic exposure will also spend more time in the hospital. This is not only a cause of school absences, but also a time of trauma for a child who is constantly visiting providers for treatment. Children with cancer have a harder time keeping up with school and keeping up with their friends

## Traffic exposure and autism

Autism is a spectrum of disorders that range from a severe inability to communicate and some mental disabilities to milder symptoms such as attention disorders. Some claims exist that the incidence of autism is higher for babies whose mothers spend time in ‘high traffic pollution’ areas compared to mothers who spend their pregnancy in cleaner air. In a recent study conducted by UCLA, air pollutant levels were measured for mothers who had children with autism and then compared to air pollutant levels in environments for mothers who had children without autism. This study found that babies who were exposed to higher levels of pollutants while in the womb had a 10% higher risk of autism than babies who had low levels of exposure; another finding from this study is that fine particulates had the strongest association with autism

## Epidemiology

Motor vehicle emissions are not solely a United States issue. Of the 10 cities with the most traffic, there are no cities from the United States listed. The United States also has regulations regarding what and how many emissions vehicles are allowed to emit that are on the road. This is done by the USEPA and they are currently working on new regulations. Of the countries that have vehicle emission standards, the European Union and Japan have the most strict regulations. These standards have been added because it is shown that regulating fuel economy is effective in controlling oil demands for the country as well as reducing their greenhouse emissions.
Respiratory and allergic disorders among children in Japan were studied after the implementation of new regulations were put in place and it showed the prevalence of asthma and other respiratory disorders decreased. There have also been more recent studies showing that the incidence of asthma cases worldwide is increasing in children. Much of this increase is due to the increase in NO2 which is a gas that is emitted from motor vehicles among other sources.
Across the United States, vehicle emissions make up a large portion of air pollution, especially in urban areas. An epidemiological study conducted by the National Institute of Health compared pregnancy loss to local vehicle emissions, specifically nitrogen dioxide (NO₂). The study used data from Boston, Massachusetts and Tel Aviv, Israel, and both regions observed associations between pregnancy loss and NO₂, largely in the second trimester of pregnancies. This study further increases scientific confidence that vehicle emissions can be detrimental to pregnant individuals and fetuses and that these findings are consistent in different geographic locations and among different populations.