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Air pollution exposure during pregnancy and reduced birth size: a prospective birth cohort study in Valencia, Spain

Findings from this mother and birth cohort study in Valencia, Spain, suggest that prenatal exposure to outdoor air pollution, measured as NO2, affects the anthropometric development of the fetus, reducing its length and head circumference and increasing the risk of having a small for gestational age (in weight) baby.

Background: Maternal exposure to air pollution has been related to fetal growth in a number of recent scientific
studies. The objective of this study was to assess the association between exposure to air pollution during
pregnancy and anthropometric measures at birth in a cohort in Valencia, Spain.
Methods: Seven hundred and eighty-five pregnant women and their singleton newborns participated in the study.
Exposure to ambient nitrogen dioxide (NO2) was estimated by means of land use regression. NO2 spatial
estimations were adjusted to correspond to relevant pregnancy periods (whole pregnancy and trimesters) for each
woman. Outcome variables were birth weight, length, and head circumference (HC), along with being small for
gestational age (SGA). The association between exposure to residential outdoor NO2 and outcomes was assessed
controlling for potential confounders and examining the shape of the relationship using generalized additive
models (GAM).
Results: For continuous anthropometric measures, GAM indicated a change in slope at NO2 concentrations of
around 40 μg/m3. NO2 exposure >40 μg/m3 during the first trimester was associated with a change in birth length
of -0.27 cm (95% CI: -0.51 to -0.03) and with a change in birth weight of -40.3 grams (-96.3 to 15.6); the same
exposure throughout the whole pregnancy was associated with a change in birth HC of -0.17 cm (-0.34 to -0.003).
The shape of the relation was seen to be roughly linear for the risk of being SGA. A 10 μg/m3 increase in NO2
during the second trimester was associated with being SGA-weight, odds ratio (OR): 1.37 (1.01-1.85). For SGAlength
the estimate for the same comparison was OR: 1.42 (0.89-2.25).
Conclusions: Prenatal exposure to traffic-related air pollution may reduce fetal growth. Findings from this study
provide further evidence of the need for developing strategies to reduce air pollution in order to prevent risks to
fetal health and development.

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