A new study from Spain reveals that babies born to mothers exposed to higher levels of air pollution during pregnancy show signs of slower brain myelination, a subtle but telling change in the way the brain’s early wiring unfolds.
Study: Unraveling the effects of prenatal air pollution on newborn brain maturation. Image credit: PeopleImages/Shutterstock.com
A recent study published in Environment International suggests that prenatal exposure to air pollution is associated with delayed maturation in the newborn, possibly related to a slowing of the rate of myelination.
Import
The developing brain is very vulnerable to injury from environmental factors, including air pollution. This can cause neuropsychiatric disorders, which are among the major causes of disability worldwide.
Particulate matter 2.5 µm or smaller (PM2.5) is often used as a pollution indicator because it comes from so many different pollution sources and contains a range of pollutants, including potentially toxic elements and essential trace elements such as iron, copper and zinc. It is easily inhaled and particles can cross the blood-brain barrier, causing adverse effects on the brain.
Prenatal exposure to PM2.5 affects fetal development. Instead, it exposes the fetus to essential micronutrients such as copper, iron and zinc, which promote white matter myelination during pregnancy. Little is known about the effect of these contrasting exposures on the brain, reflecting the complex fetal response to pollution.
For example, the offspring of women exposed to particles of the PM10 variety had larger cerebral ventricles and cerebellum. The opposite was true for exposure to NO2, although both are pollutants. Opposite effects have been reported in other brain regions.
Myelination is an important marker of brain maturation. It involves the formation of myelin sheaths around the axons of neurons. The myelin sheath speeds nerve conduction and shapes the brain’s circuits. Myelination starts in the basic pathways of the brain and progresses to higher circuits, which is reflected in the individual’s behavioral development.
Exposure to air pollution before birth causes changes in the brain’s white matter, including its myelin content and structure. This led to the current study, which examined PM2.5 exposure during pregnancy as a predictor of neonatal brain myelination.
About the study
The study sample included 93 neonates born in three hospitals in Barcelona, Spain between 2018 and 2021. Their prenatal exposure to PM2.5 was modeled, separately for the fetal and late fetal phases. The newborn brain was imaged by magnetic resonance imaging (MRI) at 29 days of postnatal life.
Study findings
Infant age at the time of MRI was associated with brain volume and overall myelination, indicating the ability to capture short-term neonatal brain development. However, this correlation was not found for cortical myelination.
Increasing prenatal PM2.5 exposure in early pregnancy was associated with lower myelinated cortical white matter content. In late pregnancy, it was associated with lower overall myelination. There were no associations with brain volume. This suggests that the cerebral cortex and deep white matter may respond differently to chemical pollution at early developmental stages.
This pattern was also observed with trace element exposure, although the associations weakened or disappeared when adjusted for confounders.
The findings suggest a delay in early myelination after prenatal exposure to air pollution. However, since myelination is a dynamic process whose rate varies with age, brain region, and nutritional availability, this observation does not necessarily indicate a deleterious or permanent effect on the fetus.
In fact, a previous study shows that slower but more prolonged white matter myelination is found in children with higher cognitive skills. The apparently slower maturation occurred during the first year of life, while a catch-up phase occurred in the following year.
Again, the placenta can protect the fetus from certain pollutants, which allows essential elements to pass through at the same time.
conclusions
Women exposed to air pollution during pregnancy had babies with lower white matter myelination in the neonatal period. Reduced cortical myelination was specifically associated with higher PM2.5 exposure in early pregnancy, but overall myelination decreased with later exposure. These findings suggest a possible delay in the maturation of the newborn’s brain.
No significant associations were found for iron, copper or zinc in PM2.5, although the observed trends were in the same direction.
The authors noted that:
This study highlights the impact of environmental factors on newborn brain development and the importance of strict air quality policies.
The cognitive outcome of late neonatal white matter myelination remains unknown. Thus, the study also highlights the importance of longitudinal research in understanding how prenatal air pollution affects long-term behavior and intellectual development.
