Prenatal Exposure to Ambient Ultrafine Particles Linked to Childhood Asthma

Pregnancy exam, pregnant woman, doctor
Pregnancy exam, pregnant woman, doctor
Prenatal exposure to ambient ultrafine particles has been linked to the development of asthma in children independent of other variables.

Prenatal exposure to ambient ultrafine particles (UFPs; <0.1 µm) has been linked to the development of asthma in children, independent of correlated pollutants such as nitrogen dioxide (NO2) and other climate variables such as temperature. A validated spatial-temporal UFP model combined with data from 2 pregnancy cohort studies that comprised a lower income, ethnically diverse urban sample from the northeastern US was used for the analysis. Results of the study were published in the American Journal of Respiratory and Critical Care Medicine.

The researchers sought to use daily UFP exposure estimates to identify suspicious windows of prenatal UFP exposure associated with the development of asthma in children, taking into consideration any sex-specific effects. Study participants included mothers and full-term (≥37 weeks’ gestation) singleton-born children from 2 pregnancy cohorts residing in the relevant catchment area and enrolled within a specific timeframe, within which UFP estimates could be assigned over gestation and 1 year postnatally beginning January 1, 2003.

Mother-child dyads from 2 pregnancy cohorts were enrolled: the Asthma Coalition on Community, Environment and Social Stress (ACCESS) project and the Programming of Intergenerational Stress Mechanisms (PRISM). Participants in the study included 376 mother-child dyads (252 from ACCESS and 124 from PRISM) whose data on UFP exposure and childhood asthma were available.

Daily UFP exposure during pregnancy was assessed by using a spatiotemporally resolved particle number concentration prediction model. Bayesian distributed lag interaction models (BDLIMs) were used to estimate the association between daily average prenatal UFP exposure and asthma incidence, as well as differences in the magnitude and timing of effects according to the sex of the child.

Incident asthma was determined at a child’s first report of asthma (ie, 3.6±3.2 years).

Covariates in the study included maternal age, race, education, and obesity; child’s sex; NO2 and temperature averages over gestation; and postnatal UFP exposure.

Overall, 37.8% of the women enrolled in the study were Black and 43.9% were Hispanic; 52.9% of them reported a high school education or a lower level of education. Among the children, 18.4% (69 of 376) developed asthma.

The cumulative odds ratio (OR) of UFP exposure across pregnancy was 4.28 (95% CI, 1.41-15.7) per doubling of UFP level across pregnancy for the overall sample, with cumulative ORs similar in both boys and girls.

In the overall sample, the BDLIMs revealed a significant association between increased UFP exposure later in a  pregnancy (ie, between 28 and 35 weeks’ gestation) and an increased likelihood of asthma.

This study was limited by its spatiotemporal UFP land-use regression model that focused on specific zip codes in Toronto, Canada. Future research is needed to examine the association between prenatal UFP exposure and child asthma risk in additional geographic locations.

The investigators concluded that the findings from this study will be enhanced by policymakers’ considering appropriate regulations that decrease the adverse effects of UFP on childhood respiratory health.


Wright RJ, Hsu HL, Chiu YM, et al. Prenatal ambient ultrafine particle exposure and childhood asthma in the northeastern United States. Am J Respir Crit Care Med. Published online May 21, 2021. doi:10.1164/rccm.202010-3743OC