Air pollution during pregnancy may affect growth of newborn
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Maternal exposure to air pollution during pregnancy has often been linked to adverse effects on the health of the newborn. A study has just concluded in a paper published in the journal Environmental Research that the stages most sensitive to air pollution are the early and late months of pregnancy.

Thyroid hormones play a key role in fetal and child development. Recent studies have linked prenatal exposure to atmospheric contaminants with changes in thyroid hormone levels in newborns.

The present study aims to assess the association of total thyroxine (TT4) levels in newborns with weekly prenatal exposure to fine particulate matter less than 2.5 microns in diameter (PM2.5) and NO2 and to identify sensitivity windows to exposure to air pollution in different developmental stages.

This prospective cohort study included mother-child pairs. Specifically, 463 mother-child pairs with data on PM2.5 and NO2 exposure during pregnancy and TT4 levels at birth were included. PM2.5 and NO2 levels were measured by high-volume aerosol samplers and passive samplers respectively during the women's pregnancies. TT4 levels were measured in heel-prick blood samples from infants. Potential associations of PM2.5 and NO2 with TT4 levels over the entire pregnancy were assessed.

- The exposure of pregnant women to PM2.5 during pregnancy was positively associated with infant TT4 level at birth.

- DLMs identified three different sensitivity windows, one in the periconceptional period with a negative association between PM2.5 exposure and TT4 levels at birth, and a second (weeks 12–17) and a third one (weeks 31–37) with a positive association.

- In addition, the later the exposure, the stronger the association. In contrast, no association was observed between NO2 exposure and TT4 levels.

The results indicate that prenatal exposure to PM2.5 could lead to a thyroid function impairment in newborns.

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