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Air pollution during pregnancy has a significant impact on the healthy development of the unborn child. A French study of 1,500 pregnant women also highlights different periods of susceptibility to pollutants depending on the sex of the fetus.
Pollution has an impact but by what mechanism?
External pollution presents a risk for the smooth progress of the pregnancy. Numerous studies have thus linked this exposure to the origin of cardio-metabolic, respiratory or even neuropsychological pathologies in the unborn child. But beyond the physiological effects, the mechanisms at play are still poorly understood.
To study this impact, research can be based on the placenta. Very vulnerable to many chemical compounds, it is a witness to the child’s prenatal environment and in fact, the epigenetic modifications occurring in its cells partly reflect the environmental exposures of the mother during pregnancy. Epigenetic modifications basically constitute an evaluation of the impact of the environment on gene expression. To evaluate these modifications, researchers measure the level of DNA methylation, one of the best-known epigenetic mechanisms involved in the control and expression of genes.
A research team led by Johanna Lepeule, Inserm researcher, at the Institute for the Advancement of Biosciences was interested in the impact of three air pollutants – nitrogen dioxide (NO2), and fine particles (PM2.5 and PM10) – on placental DNA methylation, on more than 1,500 participants during their pregnancy.
Its results show a significant impact of exposure to three air pollutants on placental DNA methylation levels concerning genes involved in fetal development. A third of these modifications were directly associated with indicators of child development (birth weight and height, head circumference, duration of pregnancy, etc.).
Other placental changes involved genes involved in the development of the nervous system, immune system and metabolism – including genes involved in the occurrence of neonatal diabetes or obesity.
A different impact depending on the sex of the baby
The researchers also identified two different gestation periods that are particularly vulnerable to epigenetic modifications under the effect of pollutants emerging in this work: the beginning of pregnancy (1st trimester) in boys and the end of pregnancy (3rd trimester) in girls. “Our results show that exposure to air pollution during pregnancy induces changes in placental DNA methylation specific to each of the two sexes, indicates Johanna Lepeule. This differentiated impact could contribute to different alterations in the development and course of pregnancy depending on the sex of the unborn child.“.
In boys, pollution could impair the development of the nervous system and intellect. “These observations support the growing number of studies associating exposure to air pollution during pregnancy and damage to neurodevelopment and/or a reduction in cognitive abilities, with greater vulnerability of male children.“, specifies Lucile Broséus, Inserm researcher and first author of the publication.
In girls, fetal development and the regulation of oxidative stress would be affected. “They could thus be associated with developmental defects likely to increase the risks of developing chronic metabolic diseases (hypertension, diabetes, obesity, etc.) later in life, but also with the occurrence of miscarriages or pre-eclampsia. at the mother’s” specifies the Inserm press release.
Future studies will have to show whether these alterations result in different development in children and whether these results specific to a French cohort can be extrapolated to other populations. However, they now demonstrate the significant impact of pollution on the in utero development of the child.
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