According to Gram Research analysis, air pollution during pregnancy may interfere with how women’s bodies process folate, a critical vitamin for baby development. A Canadian cohort study of 1,983 pregnant women found that higher air pollution exposure in the third trimester was linked to lower levels of active folate and higher levels of unprocessed folic acid, with ozone being the primary pollutant responsible. The effects were strongest among women carrying female fetuses, suggesting pregnancy sex may influence pollution’s impact on folate metabolism.
A major Canadian study of nearly 2,000 pregnant women found that breathing polluted air during pregnancy may affect how the body uses folate, a crucial vitamin for baby development. Researchers measured air pollution levels at women’s homes and tracked their folate levels across pregnancy. They discovered that higher air pollution—especially ozone—was linked to changes in folate metabolism, particularly in the third trimester and among women carrying female babies. While folate supplements help, the study suggests air quality during pregnancy may play an unexpected role in how well the body processes this essential nutrient.
Key Statistics
A 2026 cohort study of 1,983 pregnant Canadian women found that higher air pollution exposure in the third trimester was associated with 12 nanomoles per liter higher total folate but 2.8% lower active folate (5MTHF), with ozone as the primary pollutant component.
Among pregnant women in the third trimester, air pollution exposure was linked to 13.4% higher unmetabolized folic acid (UMFA), suggesting the body was less efficiently converting folate supplements into usable forms.
The association between air pollution and altered folate metabolism was significantly stronger in pregnant women carrying female fetuses compared to those carrying male fetuses, indicating fetal sex may influence pollution’s metabolic effects.
In the first trimester, air pollution showed no significant association with maternal folate status, but by the third trimester, the pollution mixture was positively associated with total folate and negatively associated with the active folate form the body uses.
The Quick Take
- What they studied: Whether air pollution affects how pregnant women’s bodies process and use folate, a vitamin critical for baby brain development
- Who participated: Nearly 2,000 pregnant women from 10 Canadian cities between 2008 and 2011, tracked from early pregnancy through the third trimester
- Key finding: In the third trimester, higher air pollution exposure was linked to higher total folate but lower amounts of the active form the body uses, with ozone being the main culprit
- What it means for you: Pregnant women in areas with poor air quality may need closer monitoring of folate status, though taking prenatal vitamins remains important. This doesn’t change current recommendations but highlights another reason to reduce air pollution exposure during pregnancy.
The Research Details
Researchers followed nearly 2,000 pregnant women across Canada from 2008 to 2011, measuring the air quality at their homes for six months before their first trimester visit and again before their third trimester visit. They measured four types of air pollution: nitrogen dioxide (from car exhaust), ozone (smog), fine particles (PM2.5), and sulfur dioxide (from industrial sources). At two points during pregnancy, they took blood samples to measure different forms of folate in the women’s bodies. The researchers used advanced statistical methods to look at how the mixture of all these pollutants together affected folate levels, rather than studying each pollutant separately.
This approach is important because pregnant women are exposed to multiple air pollutants at the same time, not just one. By studying the pollution mixture as a whole, researchers can better understand real-world exposure. Folate is essential for preventing birth defects and supporting brain development, so understanding what affects how the body uses it during pregnancy is crucial for protecting babies.
This study is strong because it followed women prospectively (tracking them forward in time rather than looking backward), measured actual air pollution at their homes rather than guessing, and took blood samples at specific pregnancy stages. The researchers used sophisticated statistical methods designed for studying multiple pollutants together. However, the study is observational, meaning it shows associations but cannot prove that pollution directly causes folate changes. The sample included only Canadian women, so results may not apply everywhere.
What the Results Show
In the third trimester, higher air pollution exposure was linked to higher total folate levels in the blood (an increase of 12 nanomoles per liter for each step up in pollution). However, this wasn’t good news: the pollution was associated with lower amounts of 5-methyltetrahydrofolate (5MTHF), which is the active form the body actually uses. At the same time, pollution was linked to higher amounts of unmetabolized folic acid (UMFA), meaning the body wasn’t converting the folate supplement into the usable form as efficiently. These associations were much stronger in the third trimester than the first trimester, suggesting pregnancy progresses and pollution effects accumulate. Ozone, the main component of smog, was the primary pollutant driving these changes.
The effects were notably stronger among women carrying female fetuses compared to those carrying male fetuses. This sex-based difference is interesting but not fully understood—it suggests that pregnancy with female babies may involve different biological responses to air pollution. The findings were consistent even after accounting for whether women were taking folic acid supplements, indicating that pollution affects folate metabolism independently of supplementation.
This is the first study to directly examine whether air pollution affects maternal folate status during pregnancy. Previous research showed that folic acid can reduce some harmful effects of air pollution on babies’ brains, but researchers didn’t know whether pollution actually interfered with folate metabolism. This study fills that gap by showing that air pollution may indeed disrupt how efficiently the body processes and uses folate, which could explain why adequate folate is so protective during pregnancy in polluted areas.
The study measured air pollution at women’s homes but didn’t track their actual movement throughout the day, so exposure estimates may not be perfectly accurate. The researchers could only study women who completed blood tests at both visits, which may have excluded some participants. The study is observational, so while it shows associations, it cannot prove that pollution directly causes folate changes—other factors could be involved. Results are from Canada, so they may not apply to other countries with different pollution types or pregnancy populations.
The Bottom Line
Pregnant women should continue taking prenatal vitamins with folic acid as recommended by their healthcare providers—this study doesn’t change that advice. Women living in areas with poor air quality should consider additional steps to reduce exposure, such as checking air quality forecasts and limiting outdoor activity on high-pollution days. Healthcare providers may want to monitor folate status more closely in pregnant women with significant air pollution exposure, particularly in the third trimester. Confidence in these recommendations is moderate, as this is the first study of its kind.
Pregnant women, especially those living in urban areas or regions with air quality concerns, should be aware of these findings. Healthcare providers caring for pregnant women should consider air quality as one factor affecting folate metabolism. Public health officials should recognize this as another reason to improve air quality. Women planning pregnancy in polluted areas may want to discuss folate monitoring with their doctors. This doesn’t apply to non-pregnant people, as the effects may be specific to pregnancy.
Air pollution’s effects on folate appear to build up over time, with stronger associations in the third trimester than early pregnancy. This suggests that reducing air pollution exposure throughout pregnancy, especially in later months, may be important. Benefits of improved air quality wouldn’t be immediate but would accumulate over weeks and months of pregnancy.
Frequently Asked Questions
Does air pollution affect folate levels during pregnancy?
Research shows that air pollution, particularly ozone, may disrupt how pregnant women’s bodies process folate. A 2026 Canadian study of nearly 2,000 women found that higher pollution in the third trimester was linked to lower active folate and higher unprocessed folic acid, suggesting pollution interferes with folate metabolism.
Should I take extra folic acid if I live in a polluted area while pregnant?
Continue taking your prenatal vitamin with folic acid as prescribed—this study doesn’t change that recommendation. However, discuss with your healthcare provider whether additional folate monitoring is appropriate if you live in an area with poor air quality, especially in your third trimester.
When does air pollution most affect folate during pregnancy?
Air pollution’s effects on folate metabolism appear strongest in the third trimester rather than early pregnancy. The Canadian study found significant associations in the third trimester but not the first, suggesting effects accumulate as pregnancy progresses.
Does fetal sex matter for how air pollution affects folate?
The study found stronger associations between air pollution and altered folate metabolism in women carrying female fetuses compared to male fetuses. The reason for this sex-based difference isn’t yet understood but suggests pregnancy with female babies may involve different biological responses to pollution.
What can I do to reduce air pollution exposure during pregnancy?
Check daily air quality forecasts for your area and limit outdoor activity on high-pollution days. Keep windows closed during poor air quality events, use air filters in your home, and consider indoor exercise alternatives. Discuss air quality concerns with your healthcare provider at prenatal visits.
Want to Apply This Research?
- Log daily air quality index (AQI) readings for your location alongside prenatal vitamin intake and any pregnancy symptoms. Track the specific AQI number and note days when you limited outdoor activity due to poor air quality.
- Set up air quality alerts on your phone for your zip code. On days when AQI exceeds 100 (unhealthy), plan indoor activities and limit outdoor exercise. Log these adjustments in the app to build awareness of your exposure patterns.
- Create a monthly summary showing your average AQI exposure and days of high pollution. Share this with your healthcare provider at prenatal visits, especially in the third trimester, to discuss whether additional folate monitoring is warranted.
This research shows associations between air pollution and folate metabolism but cannot prove direct causation. These findings do not change current recommendations for prenatal folic acid supplementation. Pregnant women should continue taking prenatal vitamins as prescribed by their healthcare providers and discuss any concerns about air quality exposure with their doctor. This study was conducted in Canada and may not apply to all populations or geographic regions. Individual circumstances vary, and personalized medical advice from a qualified healthcare provider is essential for pregnancy care decisions.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.