air pollution

Early‑Pregnancy Exposure to Fine Particulate Air Pollution Linked to Lower Birthweight in New ECHO Study

Posted on by Jodi Snare

Exposure to fine particulate matter (PM2.5)—tiny inhalable particles found in air pollution—during the earliest weeks of pregnancy was associated with babies being slightly smaller for gestational age, according to a new ECHO Cohort study led by Whitney Cowell, MPH, PhD, of NYU Langone Health.

Low birthweight is a known risk factor for a range of health issues in infancy and later life. Prior studies have shown links between PM2.5 exposure and birth outcomes, but many examined average exposure over time, leaving uncertainty about which specific weeks may be most harmful. This study aimed to pinpoint sensitive windows in early pregnancy when exposure may have the greatest impact.

Using data from 16,868 pregnant women at ECHO Cohort sites across the United States, researchers estimated weekly PM2.5 exposure during pregnancy and analyzed how it related to birthweight. They also evaluated whether associations varied by infant sex, parent race and ethnicity, or region the mother lived in during pregnancy.

Key takeaways:

  • Higher PM5 exposure during early pregnancy—particularly weeks 1–5—was associated with lower birthweight.
  • Male newborns appeared more sensitive to these early‑pregnancy exposures than female newborns.
  • Effects varied by U.S. region, with stronger associations in the Northeast, South, and Midwest, and weaker effects in the West—likely due to differences in particle types.

“The findings from this study support the need to periodically reevaluate National Ambient Air Quality Standards to ensure recommendations protect the health of the most sensitive subgroups, including pregnant women and fetuses,” said study author Dr. Cowell.

Understanding precisely when fetuses are most vulnerable to air pollution can help guide public health strategies and shape future investigations into biological mechanisms. The findings highlight the need for closer examination of pollutant composition, maternal factors, and other influences—such as diet or lifestyle—that may modify risk.

This collaborative research, titled “PM2.5 in relation to birthweight: exploring windows of susceptibility in the ECHO Cohort,” was published in JAMA Network Open.

Air Quality

ECHO Air Quality

Air Quality

The ECHO Program’s uniquely diverse, nationwide research network includes more than 64,000 children and families. It allows researchers to investigate how air quality—both indoors and outdoors—can influence children’s health and development from pregnancy through adolescence.

ECHO Discovery
Webinar Recordings

Air pollution and temperature as spatial factors impacting child health

 

Where there’s smoke… there’s action? What ECHO can do to protect children from wildfire smoke

Resources

Visit these sites to learn more about air pollution exposure.

EPA: Air Quality

NIEHS: Air Pollution and Your Health

National Weather Service: Why Air Quality is Important

QUESTIONS

For more information, please email the NIH at NIHKidsandEnvironment@od.nih.gov.
For media inquiries or to request an interview, contact Rebekah Yeager at rebekah.yeager@nih.gov. 

Air quality plays an important role in children’s health and development. Outdoor factors like green space and ambient air pollution, along with indoor conditions such as home air quality, dampness, and early-life exposure to pets, can affect breathing, brain development, pregnancy and birth outcomes, and behavior. ECHO researchers examine how exposures, including wildfire smoke, secondhand smoke, and pollution from vehicles and industrial sources, work together with home and outdoor environments to influence children’s health.

What We're Learning

The ECHO Program has published more than 2,000 articles about the results of its research, covering a wide range of topics. Many of these studies have focused on exposure to air pollution during pregnancy and early childhood. 

Here are some research highlights:

Higher Early-Life PM2.5 Linked to Higher Childhood Blood Pressure, While Prenatal NO2 Exposure Associated with Lower Blood Pressure, ECHO Study Finds
December 23, 2025
Children exposed to higher levels of certain air pollutants around birth had small differences in blood pressure later in childhood, with early pregnancy emerging as a particularly sensitive period.

Wildfire Smoke Exposure May Be Linked to Higher Risk of Preterm Birth, ECHO Study Finds
November 3, 2025
Nearly all pregnant participants were exposed to wildfire smoke, and higher exposure—especially during mid-to-late pregnancy—was linked to a slightly increased risk of preterm birth, particularly in the Western U.S.

The BREATHE Study: Bronchiolitis Recovery and Use of HEPA Filters
October 27, 2025
This clinical trial tested the use of HEPA filters in homes and and found lower indoor air pollution and somewhat fewer breathing problems and unscheduled doctor visits among babies.

ECHO Study Observes Health Disparities in Air Pollution-associated Risk of Childhood Asthma
August 1, 2025
Higher exposure to fine particulate matter, nitrogen dioxide, and ground-level ozone was linked to a higher risk of asthma in children’s first 10 years, with certain communities facing greater risk.

Prenatal Exposure to Air Pollution Associated with Higher Risk for Autism-related Outcomes, ECHO Study Finds
June 11, 2025
Children whose mothers were exposed to higher levels of air pollution during pregnancy showed a greater risk of autism-related traits and diagnosis, though patterns varied across regions.

 

Read More ECHO Research Related to Upper and Lower Airway

Exposure to PM2.5 Air Pollution During Pregnancy Associated with Lower Birthweight, ECHO Study Finds

<< Back to Research Summaries

Exposure to PM2.5 Air Pollution During Pregnancy Associated with Lower Birthweight, ECHO Study Finds

Authors: Daniel Enquobahrie, Adaeze Wosu Nzegwu, et al.

 

Who sponsored this study?

The Environmental influences on Child Health Outcomes (ECHO) Program, Office of the Director, National Institutes of Health supported this research.

 

Why was this study needed?

Exposure to fine particulate matter (PM2.5)—very small inhalable particles found in air pollution—is widespread and linked to various health risks. Previous research has examined the effects of PM2.5 exposure during pregnancy on birth outcomes, but gaps remain. More research is needed to understand whether there are critical windows during pregnancy when PM2.5 exposure is most impactful. This study aimed to address these gaps by investigating how the timing of PM2.5 exposure affects birth outcomes, such as birthweight and length of pregnancy, using data from the ECHO Cohort’s large, multi-site study structure. It also explored whether associations differ by infant sex and maternal race and ethnicity.

 

What were the study results?

Exposure to higher levels of PM2.5 during the first weeks of pregnancy was linked to babies being slightly smaller at birth and having a higher chance of being born small for their gestational age (smaller than average for the length of the pregnancy). There was no significant association between PM2.5 exposure and shorter pregnancies or preterm birth. For baby girls, higher PM2.5 exposure in early pregnancy seemed to affect their birth size more than for baby boys, suggesting that the baby's sex can make a difference in how air pollution affects growth. The effects of PM2.5 on birth outcomes like being born prematurely, birth size, or being small for gestational age varied depending on the mother's race and ethnicity.

 

What was this study's impact?

This study on PM2.5 exposure during early pregnancy and birth outcomes can inform ongoing discussions on strategies for reducing PM2.5 air pollution.

 

Who was involved?

The study included 19,108 mother-infant pairs from 51 ECHO Cohort Study Sites across the United States.

 

What happened during the study?

Researchers estimated PM2.5 exposure for each pregnant participant based on residential address, accounting for moves during pregnancy. The researchers then assessed exposure for the whole pregnancy, each trimester, and specific windows in the first trimester. The researchers collected information on birth outcomes, including length of pregnancy and birthweight.

Footnote: Results reported here are for a single study. Other or future studies may provide new information or different results. You should not make changes to your health without first consulting your healthcare professional.

 

What happens next?

Further research could help investigators better understand the mechanisms underlying differences in air pollution vulnerability by infant sex, and by maternal race and ethnicity. Additional studies could also help researchers understand how other factors, such as diet and lifestyle, influence the relationship between PM2.5 exposure and birth outcomes.

 

Where can I learn more?

Access the full journal article, titled “Gestational fine particulate matter exposure and perinatal outcomes in the ECHO cohort: Associations across pregnancy windows,” in Environmental Research.

 

The content is the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

 

Published March 1, 2026

Read the associated article.

Download this summary

Exposure to PM2.5 Air Pollution During Pregnancy Associated with Lower Birthweight, ECHO Study Finds

Read More Related Research Summaries

Pre-, Peri-, and Postnatal

ECHO Study Finds Exposure to Air Pollution During Early Pregnancy Associated with Lower Birthweight

Posted on by Jodi Snare

Exposure to fine particulate matter (PM2.5)—very small inhalable particles found in air pollution—during early pregnancy was associated with babies being slightly smaller at birth, according to a new ECHO Cohort study led by Daniel Enquobahrie, PhD, MD, MPH of the University of Washington School of Public Health and Adaeze Wosu Nzegwu, PhD, MPH of Johns Hopkins Bloomberg School of Public Health.

Exposure to PM2.5 is widespread and linked to various health risks, including respiratory, cardiovascular, and metabolic diseases. Previous research has examined the effects of PM2.5 exposure during pregnancy on birth outcomes, but gaps remain. More research is needed to understand whether there are critical windows during pregnancy when PM2.5 exposure is most impactful. For this study, researchers used information from 19,108 mothers and their babies from 51 ECHO Cohort Study Sites across the United States to evaluate how timing of PM2.5 exposure affects birth outcomes. They also explored whether associations differ by infant sex and maternal race and ethnicity.

Key Takeaways include:

  • Exposure to higher levels of PM2.5 during the first weeks of pregnancy was linked to babies being slightly smaller at birth and having a higher chance of being born small for their gestational age (smaller than average for the length of pregnancy).
  • There was no significant association between PM2.5 exposure and shorter pregnancies or preterm birth.
  • For baby girls, higher PM2.5 exposure in early pregnancy seemed to affect their birth size more than for baby boys, suggesting that the baby's sex can make a difference in how air pollution affects growth.
  • The effects of PM2.5 on birth outcomes like being born prematurely, birth size, or being small for gestational age varied depending on the mother's race and ethnicity.

“This study on PM2.5 exposure during pregnancy and birth outcomes can inform ongoing discussions on regulations that impact PM2.5 exposure, such as traffic-related air pollution.” said Dr. Enquobahrie.

Further research could help investigators better understand the mechanisms underlying differences in air pollution vulnerability by infant sex, and by maternal race and ethnicity. Additional studies could also help researchers understand how other factors, such as diet and lifestyle, influence the relationship between PM2.5 exposure and birth outcomes.

This collaborative research, titled “Gestational fine particulate matter exposure and perinatal outcomes in the ECHO cohort: Associations across pregnancy windows,” is published in Environmental Research.

Read the research summary.

Housing Conditions and Outdoor Air Pollution Together Affect Children’s Asthma Risk, New ECHO Study Shows

Posted on by Jodi Snare

Children growing up in homes with water damage or dampness and exposed to higher levels of outdoor air pollution during early childhood face a greater risk of developing asthma, according to new research supported by the NIH’s Environmental influences on Child Health Outcomes (ECHO) Program. The large multisite study found that early-life exposure to fine particulate matter (PM2.5) and indoor housing problems each independently raised asthma risk, while having a dog during infancy was linked to reduced risk.

Asthma affects millions of U.S. children, yet the environmental origins of the disease are complex. While previous research has tended to study exposures such as pollution or indoor allergens separately, this study shows that evaluating them together offers a more accurate picture of children’s risk. The ECHO Program, which brings together data from diverse U.S. populations, made this integrated analysis possible.

Drawing on data from 6,413 children across nine U.S. ECHO Study Sites, the research provides one of the clearest looks yet at how multiple early-life environmental factors interact to influence childhood asthma. The findings underscore the importance of assessing both indoor and outdoor environments together, rather than in isolation — an approach that prior studies often could not address due to limited sample sizes.

“Our research shows that to truly understand and prevent childhood asthma, we need to look at a child’s full environment—both the air they breathe outside and the conditions inside their home,” said Akihiro Shiroshita, a study author from Vanderbilt University School of Medicine. “Considering these factors together gives us a much clearer picture of what puts children at risk and how we can better protect them.”

Key Findings

  • Outdoor air pollution matters: Higher early life exposure to PM2.5 was associated with increased asthma risk.
  • Indoor environments matter too: Home dampness or water damage independently raised asthma risk, even after accounting for pollution exposure.
  • Pets may offer protection: Having a dog in the home during infancy was linked to a lower risk of developing asthma.
  • Large, diverse dataset: The study combines data from multiple U.S. ECHO Study Sites, offering a comprehensive view of environmental impacts on children’s respiratory health.

Researchers evaluated children’s exposure to PM2.5 during the first three years of life and combined that information with detailed data on early life housing conditions — including water damage, dampness, pet exposure, and dust mites. Childhood asthma was identified based on caregiver reports or physician diagnosis between birth and age five. The analysis also controlled for family and neighborhood factors to isolate the effects of environmental exposures.

The findings signal the need for additional research into how indoor and outdoor exposures interact and how early life interventions could help reduce asthma risk in children nationwide.

This collaborative research was published in Environmental Epidemiology.

About ECHO
The ECHO Cohort Consortium is a research program supported by the National Institutes of Health (NIH) with the mission to enhance the health of children for generations to come. ECHO Cohort investigators study the effects of a broad range of early environmental influences on child health and development. For more information, visit echochildren.org.

Media Contacts

For information or to request an interview, contact Rebekah Yeager,  rebekah.yeager@nih.gov.

If you are not a member of the media, but have a general inquiry, please contact  NIHKidsandEnvironment@od.nih.gov.

Connect With Us

echo connector

Check out the recent issues of our bi-monthly newsletter, the ECHO Connector, for program news and the latest research findings.

To receive the ECHO Connector through email, subscribe here.

Follow the ECHO Program on LinkedIn and X for the latest updates.

Prenatal and Early-Life Pollution Exposures May Influence Childhood Blood Pressure Patterns, ECHO Study Finds

Posted on by Jodi Snare

A child’s blood pressure may be influenced by exposure to air pollution before and shortly after birth, according to a new study from the NIH-funded Environmental influences on Child Health Outcomes (ECHO) Program. The study focused on fine particulate matter (PM2.5) and nitrogen dioxide (NO2), common pollutants from vehicles, power plants, and other industrial sources.

High blood pressure in children is becoming more common worldwide and can lead to long-term health problems, including heart disease and impaired kidney function. Over the past two decades, childhood hypertension has increased by nearly 80 percent, particularly in countries with higher obesity rates, such as the United States. Because the roots of adult hypertension often begin in childhood, ECHO researchers examined whether early exposure to outdoor air pollution may influence blood pressure in children.

Air pollutants such as PM2.5 and NO2 are known contributors to cardiovascular disease in adults, but their effects on children’s blood pressure are less well understood. Previous studies have produced mixed results and were often limited to single locations. This ECHO study leveraged data from multiple cohort sites across the United States to better clarify these associations.

Researchers analyzed data from 4,863 children ages 5 to 12 from 20 ECHO Cohort Study Sites. They estimated outdoor air pollution exposure at participants’ home addresses during each trimester of pregnancy, across the full pregnancy, and during the child’s first two years of life. Children’s blood pressure was measured during study visits and compared with typical values for children of the same age, sex, and height. Blood pressure was considered high if it fell within the top 10 percent of these values.

Key Findings

  • PM2.5 exposure and higher blood pressure: Children who were exposed to higher levels of PM2.5 before and after birth had higher blood pressure on average between ages 5 and 12.
  • Early pregnancy as a sensitive period: Higher PM2.5 exposure during the first trimester was associated with a more pronounced systolic blood pressure and a greater likelihood of high blood pressure in childhood, indicating that early pregnancy may be a particularly sensitive period.
  • Unexpected findings for NO2: Higher maternal exposure to NO2 during pregnancy was associated with slightly lower blood pressure in children. This association was strongest during mid- to late pregnancy, particularly the second trimester, and was not linked to an increased risk of high blood pressure.
  • Timing matters: The results suggest that the timing of pollution exposure during pregnancy may be important for understanding its impact on children’s cardiovascular health.

“These findings add to growing evidence that early-life exposure to fine particulate air pollution may affect children’s cardiometabolic health, even at relatively low levels,” said study author Yu Ni, PhD, of San Diego State University. “The unexpected findings related to nitrogen dioxide suggest that more research is needed to understand how this type of air pollution may affect children’s developing bodies, as well as whether other environmental factors could be playing a role, such as transportation noise.”

This collaborative research was published in Environmental Research.

Media Contacts

For information or to request an interview, contact Rebekah Yeager,  rebekah.yeager@nih.gov.

If you are not a member of the media, but have a general inquiry, please contact  NIHKidsandEnvironment@od.nih.gov.

Connect With Us

echo connector

Check out the recent issues of our bi-monthly newsletter, the ECHO Connector, for program news and the latest research findings.

To receive the ECHO Connector through email, subscribe here.

Follow the ECHO Program on LinkedIn and X for the latest updates.

Higher Early-Life PM2.5 Linked to Higher Childhood Blood Pressure, While Prenatal NO2 Exposure Associated with Lower Blood Pressure, ECHO Study Finds

<< Back to Research Summaries

Higher Early-Life PM2.5 Linked to Higher Childhood Blood Pressure, While Prenatal NO2 Exposure Associated with Lower Blood Pressure, ECHO Study Finds

Authors: Yu Ni, Catherine Karr, et al.

 

Who sponsored this study?

The Environmental influences on Child Health Outcomes (ECHO) Program, Office of the Director, National Institutes of Health supported this research.

 

Why was this study needed?

The prevalence of high blood pressure (HBP) in children is rising globally, with long-term health consequences such as heart disease and impaired kidney function. Childhood high blood pressure has increased by nearly 80% over the past two decades, especially in countries with higher obesity rates like the United States. Since high blood pressure in childhood can both track into adulthood and affect children’s health directly, ECHO researchers wanted to understand the influence that environmental factors such as pollution can have on childhood blood pressure. Specific pollutants such as fine particulate matter (PM2.5) and nitrogen dioxide (NO2) are emitted from vehicles, power plants, and industrial processes. These pollutants are known contributors to heart disease in adults, but their impact on children’s blood pressure is less clear. Previous research has been inconclusive, often limited to single-site studies. Researchers used the ECHO Cohort’s large, multi-site study structure to help clarify these associations.

 

What were the study results?

Children who were exposed to more PM2.5 air pollution before and after birth had slightly higher blood pressure on average between ages 5 and 12. Specifically, higher PM2.5 exposure during the first trimester was linked to a more pronounced increase in systolic blood pressure and a greater risk of high blood pressure in childhood, indicating that early pregnancy may be a particularly sensitive period. When their mothers were exposed to more NO2 air pollution during pregnancy, children unexpectedly had lower blood pressure. The study found that NO2 exposure during mid- to late pregnancy was associated with slightly lower blood pressure levels, particularly in the second trimester, and was not linked to a higher risk of high blood pressure. These findings overall suggest that timing of pollution exposure during pregnancy matters for children’s blood pressure later in life.

 

What was this study's impact?

The study provides additional evidence that exposure to PM2.5 may be associated with adverse effects on childhood cardiometabolic health, even at low exposure levels. The observed association between prenatal NO2 exposure and decreased childhood blood pressure is unexpected and suggests that further research may be needed to better understand the underlying mechanisms as well as other environmental factors that may influence this relationship.

 

Who was involved?

The study included 4,863 U.S. children aged 5–12 years and their mothers, drawn from 20 ECHO Cohort Study Sites.

 

What happened during the study?

Researchers estimated how much outdoor air pollution children were exposed to at their homes, focusing on PM2.5 and NO2. They examined exposure during each trimester of pregnancy, across the full pregnancy, and during the child’s first two years of life. Children’s blood pressure was measured between ages 5 and 12 and compared with typical levels for children of the same age, sex, and height; blood pressure was considered high if it fell within the top 10 percent of the distribution.

Footnote: Results reported here are for a single study. Other  studies may provide new information or different results. You should not make changes to your health or medical care without first consulting your healthcare professional.

 

What happens next?

More research could help investigators better understand why exposure to nitrogen dioxide during pregnancy was linked to lower, rather than higher, blood pressure in children. This could include exploring possible biological explanations and looking at whether other environmental exposures that occur alongside air pollution may be influencing this finding, such as transportation noise exposure.

 

Where can I learn more?

Access the full journal article, titled “Pre- and Postnatal Exposure to PM2.5 and NO2 and Blood Pressure in Children: Results from the ECHO Cohort,” in Environmental Research.

 

The content is the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

 

Published December 23, 2025

Read the associated article.

Download this summary

Higher Early-Life PM2.5 Linked to Higher Childhood Blood Pressure, While Prenatal NO2 Exposure Associated with Lower Blood Pressure, ECHO Study Finds

Read More Related Research Summaries

Pre-, Peri-, and Postnatal

Home Conditions and Outdoor Air Pollution May Together Influence Children’s Asthma Risk, ECHO Study Finds

<< Back to Research Summaries

Home Conditions and Outdoor Air Pollution May Together Influence Children’s Asthma Risk, ECHO Study Finds

Authors: Akihiro Shiroshita, et al.

 

Who sponsored this study?

The Environmental influences on Child Health Outcomes (ECHO) Program, Office of the Director, National Institutes of Health supported this research.

 

Why was this study needed?

Childhood asthma may be influenced by multiple indoor and outdoor environmental exposures. Prior research has examined indoor and outdoor exposures separately and frequently lacked the power to fully evaluate their cumulative or interacting effects on childhood asthma. The ECHO Cohort allowed researchers to bring together data from many sites across the country, providing a clearer picture of how different environmental factors may influence childhood asthma.

 

What were the study results?

The study found that several environmental exposures during early childhood were linked to asthma risk. First, exposure to ambient fine particulate air pollution (PM2.5) was associated with an increased risk of developing asthma. In addition, water damage or dampness in the home was also linked to a higher asthma risk, even after accounting for PM2.5 exposure, indicating an independent effect. In contrast, having a dog in the home during infancy was associated with a reduced risk of childhood asthma.

 

What was this study's impact?

The study demonstrated the importance of considering multiple early-life exposures together when assessing risk factors for childhood asthma. It highlighted that both indoor (home dampness, pets) and outdoor (PM2.5) exposures should be considered in prevention strategies.

 

Who was involved?

Participants included 6,413 children born between 1987 and 2016, enrolled in nine ECHO Study Sites across the United States. These sites included both general-risk and high-risk populations at higher risk, defined by a parental history of asthma or allergy.

 

What happened during the study?

The study looked at children’s early-life environments to understand how they relate to asthma risk. Researchers examined levels of outdoor air pollution during the first three years of life, along with conditions inside the home, such as water damage or dampness, whether dogs or cats were present during infancy, and exposure to dust mites. Childhood asthma was identified based on reports from caregivers or a doctor’s diagnosis between birth and age five. The analysis considered differences in family and neighborhood factors that could also affect asthma risk, helping to isolate the role of these environmental exposures.

Footnote: Results reported here are for a single study. Other or future studies may provide new information or different results. You should not make changes to your health without first consulting your healthcare professional.

 

What happens next?

Additional studies examining how indoor and outdoor exposures interact could help researchers better understand their role in childhood asthma risk. Future research could also explore ways to reduce or prevent harmful exposures in early life.

 

Where can I learn more?

Access the full journal article, titled “Individual and combined effects of indoor home exposures and ambient PM2.5 during early life on childhood asthma in US birth cohort studies,” in Environmental Epidemiology.

 

The content is the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

 

Published December 23, 2025

Read the associated article.

Download this summary

Home Conditions and Outdoor Air Pollution May Together Influence Children’s Asthma Risk, ECHO Study Finds

Read More Related Research Summaries

Upper and Lower Airway

Exposure to Fine Particulate Air Pollution in Early Pregnancy Linked to Lower Birth Weight, ECHO Study Finds

<< Back to Research Summaries

Exposure to Fine Particulate Air Pollution in Early Pregnancy Linked to Lower Birth Weight, ECHO Study Finds

Authors: Whitney Cowell, et al.

 

Who sponsored this study?

The Environmental influences on Child Health Outcomes (ECHO) Program, Office of the Director, National Institutes of Health supported this research.

 

Why was this study needed?

Babies born with low birth weight are at a higher risk for health problems both at birth and later in life. Prior research has shown that exposure to fine particulate matter (PM2.5)—very small inhalable particles found in air pollution—during pregnancy can negatively affect birth weight. Many past studies examined average exposure over pregnancy, which may miss specific windows when the baby is most sensitive. The goal of this study was to identify the specific weeks in pregnancy when babies are most vulnerable to PM2.5 exposure.

 

What were the study results?

Exposure to PM2.5 during pregnancy was associated with lower birth weight for gestational age, particularly when exposure occurred in the early weeks of pregnancy (weeks 1–5). Male newborns appeared more sensitive to exposure than females. The study also found regional differences, with stronger associations observed in the Northeast, South, and Midwest. This may relate to differences in the types of particles found in the air in these regions.

 

What was this study's impact?

This study gives us a clearer picture of when during pregnancy air pollution may be most harmful to a baby’s growth. Understanding these sensitive time periods can inform future research on what’s happening in the body during those weeks and why pollution may have a bigger impact during those times.

 

Who was involved?

The study included 16,868 pregnant participants from the ECHO Cohort, spanning 50 sites across the United States.

 

What happened during the study?

Researchers applied computer models to estimate pregnant participants' weekly exposure to PM2.5 throughout their pregnancies. Birth weight was recorded at the time of delivery and then standardized using national growth charts to account for variations in gestational age (length of pregnancy).  Analysts used statistical methods to identify how overall and week-specific PM2.5 exposure related to birthweight. These methods also tested whether the impact of PM2.5 differed by the baby’s sex, race or ethnicity of the parents, or the region of the country the mother lived in during pregnancy.

Footnote: Results reported here are for a single study. Other or future studies may provide new information or different results. You should not make changes to your health without first consulting your healthcare professional.

 

What happens next?

Future studies could help explain how different types and sizes of pollution particles affect baby’s growth. Additional research could also help identify the periods of pregnancy when reducing exposure would have the greatest impact.

 

Where can I learn more?

Access the full journal article, titled “PM2.5 in relation to birth weight: exploring windows of susceptibility in the ECHO Cohort,” in JAMA Network Open.

 

The content is the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

 

Published December 1, 2025

Read the associated article.

Download this summary

Exposure to Fine Particulate Air Pollution in Early Pregnancy Linked to Lower Birth Weight, ECHO Study Finds

Read More Related Research Summaries

Pre-, Peri-, and Postnatal

Exposure to Air Pollution During Pregnancy Associated with Higher Risk for Autism-related Outcomes

Posted on by Jodi Snare

Exposure to certain air pollutants during pregnancy was associated with autism-related traits and increased odds of autism spectrum disorder (ASD) diagnosis in children, according to a recent ECHO Cohort study led by Akhgar Ghassabian, MD, PhD of NYU Grossman School of Medicine and Heather Volk, PhD of Johns Hopkins Bloomberg School of Public Health.

Air pollution is a significant environmental health concern and contributes to many illnesses and early deaths worldwide. Ambient air pollution can have detectable effects on the brain. Recent studies show that being exposed to air pollution during pregnancy and early life can affect how a child’s brain develops. This can happen through several pathways, such as causing inflammation in the brain, disrupting hormones, or changing how genes work. Previous research has suggested potential links between air pollution and neurodevelopmental disorders, but the relationship between exposure to air pollution, even at low levels, during pregnancy and ASD has been unclear.

This study included 8,035 mother-child pairs from 44 ECHO Cohort study sites, including over 1,000 children who were potentially at higher risk for ASD based on being born preterm or having siblings with autism.

Key takeaways include:

  • Prenatal exposure to ozone was associated with autism-related traits and increased risk of ASD diagnosis.
  • Exposure to fine particulate matter (PM5) and nitrogen dioxide was also associated with a higher risk of autism, but associations varied by geographical regions.
  • There was little evidence for differences between boys and girls in the association between prenatal air pollution exposure and autism outcomes.

These findings suggest that even low levels of air pollution exposure during pregnancy can be associated with autism-related outcomes. This highlights the importance of understanding the risks associated with air pollution exposure during pregnancy and its effects on neurodevelopment.

This collaborative research, titled “Prenatal Air Pollution Exposure and Autism Spectrum Disorder in the ECHO Consortium,” is published in Environmental Health Perspectives.