The highly sensitive period of preimplantation development represents that embryo is very vulnerable to exogenous agents. Many of the developmental abnormalities may arise from the inevitable maternal periconceptional exposures to toxic substances in the environment which may threaten reproductive capability and pregnancy outcomes. In this article, an overview of the association between air pollution and reproductive, fetal, and neonatal health outcomes is given.
Materials and methods
A literature search was conducted through PubMed to identify air pollution and fertility related studies.
Regardless of the consideration of different types of study design, the statistical methods used and residual uncontrolled confounding variables, critical appraisal of reported studies reveals a causal relationship between environmental air pollution exposure and reproductive functions. Among the components of air pollution, particulate matter (PM) appears to be the most harmful to human health. PM include a range of tiny particles, including acids, organic chemicals, metals, and soil or dust particles. Particles come in a wide range of sizes in which smaller size fractions (PM<10) have the highest toxicity.A series of studies showed that exposure to ambient levels of air pollutants, specifically PM were associated with fetal development. Prematurity, low birth weight, neonatal and postneonatal mortality were also reported to be associated with air pollutant exposure in some studies. It has been suggested that third-trimester exposure is most associated with an increased risk of neonatal abnormality. Air pollution may affect fetal development and birth outcomes through multiple pathways including systemic alterations in systematic oxidative stress, pulmonary and placental inflammation, maternal blood coagulation factors, hematocrit, blood viscosity and endothelial dysfunction. Altered pulmonary and cardiovascular functions may also play a fundamental role in morbidity and mortality during the postnatal period. In addition, air pollution can negatively affect male fertility by decrements in semen measures including proportionately fewer motile sperm, less sperm with normal morphology and more sperm with abnormal chromatin. Alternatively, the increased risk of early pregnancy loss has been observed in women exposed to air pollution which could be related to maternal changes in the uterine vascular environment prior to pregnancy.
Exposure to air pollution could be associated with lower fertility rates in humans and adverse birth outcomes including fetal growth, prematurity, neonatal mortality and miscarriage.