Maternal exposure to ambient air pollution is associated with development of intrauterine inflammation, which increases the risk of preterm birth
Fetal development is a critical period of life where very small factors have dramatic consequences. It is well established and understood that drinking alcohol, smoking cigarettes, or taking drugs during pregnancy can be deleterious for the developing child and consequently, those behaviors are generally avoided. However, even with an healthy lifestyle, pregnant women living in large cities such as Boston cannot escape from being exposed to air pollution. Recent evidence shows that the fetus is highly sensitive to small particles present in polluted air.
Intrauterine inflammation is an important risk factor for both preterm birth and neurodevelopmental complications. It was previously shown that exposure to ambient air pollution during pregnancy is associated with preterm birth and low birth weight. Both of these birth complications can also impact the growth, development and function of the placenta. However the direct association between intrauterine inflammation and exposure to air pollution had never been documented.
Researchers from USA and China have associated exposure to air pollution, mainly to very small air contaminants called PM2.5, with a higher level of intrauterine inflammation. Their results were published in the journal Environmental Health Perspectives. They used data from the Boston Birth Cohort collected between 1999 and 2012 including more than 5,000 mother-infant pairs. Intrauterine inflammation was assessed by measure of fever during pregnancy and presence of placenta pathology.
This new association, between intrauterine inflammation and air pollution, was possible giving the availability of sociodemographic and clinical data, combined with placental biopsies taken after birth in the Boston Birth Cohort. An interesting finding in this study is that even low levels of exposure to air pollution (9 micrograms/m3 when the US standard is 12 micrograms/m3) can induce intrauterine inflammation. They also found that exposure during the first trimester of pregnancy is the time for highest risk.
The advantage of this new association is that inflammation has clinical manifestations, such as fever. Therefore, it could allow identifying the problem early in the pregnancy in order to prevent the adverse outcomes for the fetus, by taking action to reduce mother’s exposure to PM2.5. Finally, this study highlights that the current standards for maximum level of air pollution are not appropriate for pregnant women.
Written By: Jean-Michel Bourget, PhD