Pollution's Start: Womb Or Birth?

Air pollution is a pervasive issue that has been linked to a variety of health problems, including respiratory issues, cardiorespiratory problems, and even lung cancer. Recent studies have also found a correlation between air pollution and adverse pregnancy outcomes, with evidence suggesting that exposure to air pollution during pregnancy can increase the risk of preterm birth, low birth weight, congenital abnormalities, and neonatal mortality. With the fetus being particularly susceptible to environmental contaminants during its development, the impact of pollution begins even before birth, affecting fetal growth and development and potentially predisposing individuals to diseases later in life. As such, it is crucial to recognize the role of pollution in pregnancy outcomes and to address the issue through public health policies and cleaner technologies.

Air pollution and pregnancy complications

Air pollution is an increasingly recognised health risk, with 99% of the world's population now breathing polluted air that exceeds the World Health Organization's recommended limits. The burning of fossil fuels has increased concentrations of greenhouse gases, which contribute to climate change and further worsen air pollution.

Pregnant women and their newborn infants are particularly susceptible to the effects of air pollution due to their unique physiology. During pregnancy, physiological changes include a 20% increase in oxygen consumption, a 40-50% increase in minute ventilation, and a 40% increase in cardiac output. These changes increase the amount of inhaled and circulated pollutants, thereby increasing exposure.

Maternal exposure to air pollution during pregnancy is associated with adverse birth outcomes, including low birth weight, preterm birth, congenital malformation, intrauterine growth restriction, and neonatal mortality. Furthermore, exposures are associated with increased risks for preeclampsia, hypertension, gestational diabetes, and postpartum depression.

Several studies have investigated the impact of ambient air pollution exposure during pregnancy on adverse birth outcomes. One study, conducted in Durban, South Africa, from 2013 to 2017, found that exposure to PM2.5 had significant direct and indirect effects on the risk of adverse birth outcomes. Similarly, increased levels of maternal exposure to SO2 during pregnancy were associated with an increased probability of the infant being small for their gestational age.

Another study, conducted in Boston, analysed data from 5,059 mother-child pairs and found that even exposure to air pollution levels below the EPA standard had biological effects. The researchers concluded that current US Environmental Protection Agency air pollution standards may not be sufficient to protect the developing fetus.

Overall, the evidence suggests that air pollution has significant adverse effects on pregnancy and neonatal outcomes. Local government officials have a responsibility to better control air pollution, and healthcare providers should advise pregnant women about the risks of air pollution during pregnancy.

The impact of toxins on the fetus

A range of environmental toxins can affect the embryo, fetus, or infant during development. These include pesticides, heavy metals, dioxin derivatives, and polychlorinated diphenyl compounds. Exposure to toxins such as lead, tobacco smoke, and DDT has been linked to an increased risk of miscarriage, low birth weight, and preterm birth. The impact of toxins on the fetus can also extend to later life, with potential effects on the nervous system, learning abilities, liver function, thyroid hormone levels, and white blood cell levels.

Air pollution, particularly in urban areas, has been associated with an increased risk of low birth weight, preterm birth, congenital malformations, intrauterine growth restriction, and neonatal mortality. The combustion of fossil fuels, vehicle emissions, and industrial activities release toxic compounds such as carbon monoxide, nitrogen dioxide, and sulfur dioxide, ozone, lead, and polycyclic aromatic hydrocarbons. These pollutants can be inhaled by expecting mothers, causing serious harm to the fetus.

Additionally, the presence of metal buildup in the placenta can restrict fetal growth, leading to preterm birth, increased gestational diabetes, shorter telomere length, and reduced chromosomal stability. Exposure to multiple chemicals during pregnancy can have a cumulative impact, with Bisphenol A (BPA) detected in 96% of women surveyed.

Furthermore, consuming fish with high mercury levels can harm the developing nervous system of the fetus, potentially leading to learning disabilities. A notable example is the Minamata disaster in the 1950s, where industrial mercury discharge into Minamata Bay in Japan resulted in high rates of miscarriage among pregnant women exposed to the contaminated fish.

Environmental contaminants and fetal development

Environmental contaminants can have a significant impact on fetal development, with exposure to toxins during pregnancy potentially causing an unfavourable outcome. The fetus is particularly susceptible to environmental contaminants as it is developing and is, therefore, more susceptible to their effects.

The maternal environment is a major factor in fetal growth and may even be more important than genetics. A study of pregnancies with ovum donation observed correlations between birth weight of the mother and the newborn, but no such correlation with the ovum donor.

During pregnancy, exposure to air pollution increases the risks for low birth weight, preterm birth, congenital malformation, intrauterine growth restriction, and neonatal mortality. Exposures are also associated with increased risks for preeclampsia, hypertension, gestational diabetes, and even stillbirth.

Heavy metals, in particular, can accumulate in placental transfer cells, decreasing uterine blood flow and the transfer of nutrients to the fetus, thereby affecting fetal growth and development. These metals can impair or alter the uterine environment and dysregulate the fetal epigenome. Endocrine disruptors, such as those introduced into the environment through oil and gas extraction, can also have an impact on fetal development by interacting with hormone receptors and changing hormone concentrations within the body.

In addition, environmental exposures can have an impact on childhood growth trajectories. For instance, exposure to PFCs has been linked to an increased risk of obesity, with environmental stressors potentially resulting in a 'thrifty phenotype' that stores excess calories too efficiently.

Links between pollution and asthma in children

Air pollution has been linked to a range of adverse health effects, including respiratory and cardiovascular issues, and even death. Children are especially vulnerable to the impacts of air pollution, as they breathe more air per kilogram of body weight and spend more time engaged in outdoor activities, increasing their exposure.

Several studies have found a link between air pollution and asthma in children. Asthma is a serious and life-threatening chronic respiratory disease that affects approximately six million children in the United States. Research has shown that air pollution can worsen asthma symptoms and trigger asthma attacks in children. Poor air quality can irritate children's airways, causing swelling and tightness, and leading to breathing difficulties. Additionally, pollutants can increase children's susceptibility to upper respiratory infections, which can, in turn, bring on asthma symptoms.

African American adolescents have been identified as being particularly vulnerable to the effects of air pollution. A study conducted in North Carolina found that even low levels of outdoor ozone were associated with respiratory changes in African American children with difficult-to-treat asthma, despite the use of asthma therapies.

Another study by researchers from Johns Hopkins University found that children exposed to outdoor coarse particulate matter (PM10-2.5) were more likely to develop asthma and require emergency room treatment. Coarse PM can come from roadway particles such as brake and tire wear, as well as mixtures of road dust and metals. While fine particulate matter (PM2.5) has been more commonly associated with the development of asthma, this study highlights the harmful effects of coarse PM, which can deposit into children's airways and lead to respiratory issues.

While the exact mechanisms are not yet fully understood, researchers hypothesize that air pollutants may suppress genes responsible for the immune system's ability to differentiate allergens from dangerous foreign substances. This can lead to an inflammatory response, even when the substance is not harmful, ultimately resulting in asthma.

Overall, the evidence suggests a strong link between pollution and asthma in children, highlighting the need for further research and public policies that address air quality to protect the health of vulnerable individuals.

Air quality guidelines and health risks

Air pollution is a complex mixture of solid particles, liquid droplets, and gases. It is the greatest environmental threat to health and a leading cause of non-communicable diseases (NCDs) such as heart attacks or strokes. According to the World Health Organization (WHO), there are approximately 7 million premature deaths every year due to the combined effects of outdoor and household air pollution. The air that we breathe outdoors is a major environmental health problem affecting everyone globally.

The WHO's Air Quality and Health Unit works in three cross-cutting areas to reduce air pollution levels and protect populations from health risks: knowledge, evidence, and measuring progress; institutional capacity building and technical support; and leadership and coordination. The WHO's Air quality guidelines (AQG) are a set of evidence-based recommendations of limit values for specific air pollutants, developed to help countries achieve air quality that protects public health. These guidelines are of high methodological quality and are developed through a transparent, evidence-based decision-making process. The first release of the guidelines was in 1987, and several updated versions have appeared since then, with the latest global version published in 2005. WHO updates the Air Quality Guidelines regularly to ensure their continued relevance and to support a broad range of policy options for air-quality management in various parts of the world. The 2021 update of the WHO air quality guidelines is in response to the real and continued threat of air pollution to public health.

The guidelines offer global guidance on thresholds and limits for key air pollutants that pose health risks. For example, fine particulate matter (PM2.5) can penetrate through the lungs and further enter the body through the bloodstream, affecting all major organs. Exposure to PM2.5 can cause diseases in our cardiovascular and respiratory systems, provoking, for example, stroke, lung cancer, and chronic obstructive pulmonary disease (COPD). New research has also shown an association between prenatal exposure to high levels of air pollution and developmental delay at age three, as well as psychological and behavioural problems later on, including symptoms of attention deficit hyperactivity disorder (ADHD), anxiety, and depression.

Furthermore, epidemiological and experimental evidence agree that gestational exposure to air pollution increases the risks for low birth weight, preterm birth, congenital malformation, intrauterine growth restriction, and neonatal mortality. Exposures are also associated with increased risks for preeclampsia, hypertension, and gestational diabetes. Therefore, it is crucial for the health sector to be involved in the discussion of public policies that may affect the quality of the environment and, directly or indirectly, impact the health of those who were not yet born.

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