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Prenatal exposure to fine particulate matter during pregnancy was associated with a 12% higher risk of cerebral palsy for the resulting infants, a cohort study in Canada found.

Each increase of 2.7 μg/m³ in the interquartile range (IQR) for prenatal ambient PM_2.5 (particulate matter 2.5 μm or less in diameter) concentration was associated with a cumulative hazard ratio of 1.12 (95% CI 1.03-1.21) for cerebral palsy, reported Carmen Messerlian, PhD, of the Harvard T.H. Chan School of Public Health in Boston, and co-authors in .

Risk for boy babies was higher than for girls (HR 1.14, 95% CI 1.02-1.26, vs HR 1.08, 95% CI 0.96-1.22). The increase in risk was seen only for PM_2.5, not nitrogen dioxide or ozone exposure.

"Twelve percent doesn't sound like a huge number, but in fact... these are levels that are population levels. They're not extreme levels of people that are working in factories, or a high risk group," Messerlian told MedPage Today. "This is the general population. And so this is levels of air pollution that you or I could be exposed to, our sisters or our friends could be exposed to, during their pregnancies."

Past research has identified preterm birth as a cerebral palsy, but most cerebral palsy cases are born at term. However, a higher cerebral palsy risk in pregnancies conceived in the winter or spring, compared with the summer or fall, pointing toward an environmental cause. It's also been shown that air pollutants in maternal circulation can , and that environmental exposures can affect the sensitive stages of early brain development.

"Prenatal exposure to air pollution is associated with decelerated neurological development early in life and increased risk of neurodevelopmental problems," Messerlian and colleagues wrote. "Although no animal or human study has ever reported a direct link between air pollution and CP [cerebral palsy], it is possible that air pollution may increase the risk of CP following similar pathophysiological pathways."

"Linking an environmental exposure to CP is not the typical way of thinking about disease onset," Robert Akins, PhD, of Nemours Children's Health in Delaware, who was not involved in the study, told MedPage Today. "And although the 1.12 times higher risk estimated by their analysis may seem modest to some, I think the fact that a distinct elevation was found at all may turn out to be really important."

Messerlian's group included all full-term births from hospitals in Canada's Ontario province during 2002-2017 using administrative records from ICES, a nonprofit that collects healthcare and demographic data from all residents in Ontario. Children from multiple birth pregnancies, with invalid health card numbers, missing 6-digit postal codes, missing or invalid exposure estimates, or those ineligible for provincial health insurance were excluded.

Sociodemographic and healthcare data came from various sources. To assess exposure to air pollutants, the researchers used estimates of weekly pollutant concentrations at the geographic centers of each 6-digit postal code area, from reported residential addresses at delivery. Fine particulate matter concentrations were estimated from satellite-derived estimates and ground-level monitoring data from the Canadian National Air Pollution Surveillance network, combined with certain climate, weather and topographical characteristics. Weekly concentrations of residential air pollutants throughout pregnancy were linked to recorded gestational ages.

A total of 1,587,935 mother-child pairs who reached term gestation were included. Of these, 3,171 (0.2%) were diagnosed with CP. Median age at time of CP diagnosis was 1 year. Mean maternal delivery age was 30.1 years. Boys were more prevalent in the CP group (56.3%) than the non-CP group (51.1%). Children with CP were slightly more likely to be born to mothers with a higher "regional marginalization index" and in smaller communities.

"If it's causal or not causal, that doesn't really matter. What we know is that higher levels of poor quality air can harm your baby," said Messerlian. "And so if you're planning a pregnancy or trying to get pregnant, having two things: being mindful of the air quality outside throughout your pregnancy, and reducing your exposure during peak times of poor quality air" are key. Messerlian added that air filters can help with this, too, and that educating mothers about their risks of pollutant exposure is critical.

Limitations of the study included assigning pollution exposure by residence at delivery, which could have changed during pregnancy. Researchers were also unable to assess specific subtypes of cerebral palsy. Residual and unmeasured confounding could have affected results, and the findings cannot be generalized to preterm births. Air pollution is also related to pregnancy loss, but the study included only live births. Further, air pollution in Canada is relatively low compared to the rest of the world.

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