Is air pollutant exposure during pregnancy associated with infant cerebral palsy risk?

Given the known association between exposure to air pollution and neurodevelopmental disorders involving changes in neurogenesis and brain structure, a recent study published in JAMA Network Open examined the association between prenatal exposure to ambient air pollution during the pregnancy and the risk of cerebral palsy in the infant.

Study: Prenatal Exposure to Ambient Air Pollution and Cerebral Palsy. Image Credit: Ahmet Misirligul/Shutterstock.com

Background

A large body of evidence from animal and human studies indicates that exposure to air pollution, especially fine particulate pollutants, can cause changes in brain structure and cause cognitive developmental delays.

In humans, exposure to air pollution has also been linked to autism and disorders related to structural alterations in the brain. Studies have also found that black carbon particles can cross over to the fetus through the placenta, indicating that pollutant particles in maternal circulation can impact the fetus.

Cerebral palsy is a nonprogressive neurodevelopmental disorder that has heterogeneous clinical subtypes characterized largely by physical disability and motor impairments.

The disease often also causes impairments in perception, sensation, communication, and cognitions, as well as secondary musculoskeletal impairments and epilepsy.

While pre-term birth is known to increase the risk of cerebral palsy, the cause of cerebral palsy in infants born full-term remains unclear.

The increase in cerebral palsy risk among infants born in the winter and spring months indicates a potential environmental cause.

About the study

In the present study, the researchers used population-based health data from Ontario, Canada, spanning the years between 2002 and 2017, to determine whether exposure to air pollutants during the prenatal period was linked to a higher risk of cerebral palsy in infants born full-term.

They also examined whether the windows of susceptibility changed based on the gestational weeks.

The study included all infants born full-term in Ontario between April 2002 and the end of March 2017.

The administrative health data for the analysis was obtained from the Institute for Clinical Evaluative Sciences, which is a non-profit institute that conducts research on health care and demographics in Ontario.

The Canadian Institute for Health Information’s discharge abstract database provided information on hospital admissions, while the data to ascertain outcomes was acquired from the Ontario Health Insurance Plan records.

Additionally, the researchers also used demographic characteristics and socio-economic status data by area for the study.

The weekly estimates of the concentrations of fine particulate matter of diameters less than 2.5 microns (PM_2.5) and ozone and nitrogen dioxide at the center of each participant’s geographic area of residence were used to determine prenatal exposure to air pollutants.

Geophysical satellite-derived estimates and data from ground-level monitoring were also used to estimate the concentrations of PM_2.5.

An inpatient hospitalization diagnosis of cerebral palsy or two or more outpatient diagnoses in two weeks or more were used to determine a diagnosis of cerebral palsy in the infant. Follow-ups were conducted from birthday to end of study, death, or shifting of residence to an area outside Ontario, whichever occurred first.

Confounders such as maternal age at birth, community size, season and fiscal year of birth, residential instability quintile groups, and maternal instability were used to adjust the models.

Furthermore, based on known findings about sexually dimorphic differences in cerebral palsy, the researchers also examined the association between air pollution exposure and cerebral palsy risk for heterogeneity based on the sex of the infant.

Results

The findings suggested that exposure to air pollution, especially PM_2.5, during the prenatal stage of the pregnancy was linked to a higher risk of cerebral palsy in the infant, even if the pregnancy was carried to term.

Furthermore, the risk of cerebral palsy was slightly higher for male infants than for female infants, although the difference was not statistically significant.

Additionally, although the study found no specific window of susceptibility, elevated risks of cerebral palsy, albeit imprecise, were found for exposure to PM_2.5 during the first two trimesters for male infants and the first trimester for female infants.

No associations were found between the risk of cerebral palsy and exposure to nitrogen dioxide or ozone during pregnancy.

Similar results were observed from studies examining the association between prenatal exposure to PM_2.5 and the development of neurodevelopmental disorders such as attention deficit hyperactivity disorder and autism spectrum disorder.

The researchers believe that since cortisol neurogenesis in the fetus, which involves neuronal proliferation and organization, occurs until the end of the second trimester, exposure to PM_2.5 during the first 24 weeks could result in neuronal malformations, resulting in cerebral palsy.

Conclusions

The study found that exposure to air pollution consisting of particulate matter below 2.5 microns in diameter during the prenatal period could increase the risk of cerebral palsy.

Although not significantly different, male infants were at a higher risk of cerebral palsy than female infants. Furthermore, exposure to PM_2.5 during the first two trimesters was considered especially detrimental to the neuronal development of the infant.