Overview

Evidence shows that pregnant women and babies exposed to high levels of air pollutants face an increased risk of adverse health outcomes. Adding to this concern is the rising frequency of wildfires, further threatening air quality. According to the World Health Organization, 99% of the global population breathes air that exceeds WHO air quality limits. While avoiding exposure to air pollution and wildfire smoke is the best way to limit your risk, this is not always possible. The good news is that you can reduce exposure and minimize the harmful effects with practical steps, from monitoring the Air Quality Index to using air filtration systems and supplementing with antioxidants to strengthen your body’s defenses. By focusing on the factors within your control, you can take proactive measures to protect yourself and your family from the dangers of poor air quality.

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Article and Resources

Hi Vanessa,

I just wanted to start by saying how much I love the Pregnancy Podcast! Your episodes have been such a great resource so far, and I really appreciate all of the evidence-based information.

I am in Southern California, and with the wildfires going on, it’s been a stressful time. Thankfully, where I live is currently safe from the fires, but there’s been a lot of smoke in the air. I’m worried about the air quality. I’m wondering if poor air quality is dangerous during pregnancy and if there’s anything I should be doing to protect myself and my baby.

Thank you so much for everything you do!

Best regards,
Lauren

The wildfires in the Los Angeles area are devastating, and my heart goes out to everyone affected. Any time we have wildfires, they affect air quality in the surrounding regions. Depending on the extent of the fires and the wind, the effects can range long distances. Smoke from fires in Canada has reached as far south as Florida and smoke from fires in the Western United States has reached the East Coast.

Air Pollution is a Global Concern

According to the World Health Organization, 99% of the global population breathes air that exceeds WHO air quality limits. The WHO has limits on nitrogen dioxide (NO₂), particulate matter with a diameter equal to or smaller than 10 μm (PM₁₀), and particulate matter with a diameter equal to or smaller than 2.5 μm (PM_2.5). These are the main concerns associated with air pollution.

NO₂ comes from the combustion of fossil fuels and emissions from household heating systems. This air pollutant has harmful effects on human health and the environment. Particulate matter is a broad term that includes metals, soil or dust particles, natural and synthetic chemicals, and allergens. Particulate matter with an aerodynamic diameter of less than 10μm is a concern because they are small enough to enter the lungs. Those with a diameter of less than 2.5μm are of even greater concern because they can enter the circulatory system through the lungs’ alveoli.

Another concern for air quality is O₃ or ozone, a molecule composed of three oxygen atoms. In the upper atmosphere, ozone is critical for life on Earth, absorbing most of the sun’s harmful ultraviolet radiation. Ozone can also form when pollutants react with sunlight at ground level. It is a major component of smog and a harmful air pollutant.

Pregnant Women and Babies Are More Susceptible to Poor Air Quality

Some physiological changes during pregnancy make pregnant women more susceptible to the adverse effects of poor air quality. During pregnancy, you have a 20% increase in oxygen consumption. You have a 40% to 50% increase in minute ventilation, the total volume of air you inhale and exhale from your lungs per minute. Plus, you have a 40% increase in cardiac output. If exposed to poor air quality, these changes increase the amount of pollutants you inhale and circulate, thereby increasing your exposure.

Newborns have a faster metabolism, meaning they use more oxygen and have smaller, less efficient lungs than older children and adults. Babies also breathe in more air relative to their body weight, about twice as much as adults. This means they take in more air pollutants if they are exposed to poor air quality.

The Evidence of Poor Air Quality During Pregnancy

Evidence shows that pregnant women and babies exposed to high levels of air pollutants are at increased risk of adverse health outcomes. These include maternal hypertensive disorders, postpartum depression, placental abruption, low birth weight, preterm birth, infant mortality, and adverse lung and respiratory effects. Scientists are still exploring the exact mechanisms by which air pollution exerts adverse health effects. Oxidative stress, epigenetic, and immune mechanisms are thought also to play a role.

A study over 15 years examined the effects of air pollution on adverse birth outcomes and pregnancy complications. This study measured exposure to NO₂, particulate matter, and O₃. The researchers did not observe consistent associations between adverse pregnancy and birth outcomes with exposure to PM_2.5 (particulate matter equal to or smaller than 2.5 μm). There was a positive link between increased O₃ exposure during pregnancy, especially in the second and third trimesters, and a higher risk of preterm birth and decreased birth weight. O₃ exposure in the first trimester was associated with an elevated risk of gestational hypertension. Exposure to NO₂ during the first trimester was linked to an increased risk of gestational diabetes. Like many others, this study demonstrates the significance of reducing exposure to air pollution during pregnancy.

How Wildfires Affect Air Quality

Wildfire smoke often contains higher concentrations of harmful pollutants than typical ambient air, even in a city with heavy smog. Thankfully, wildfires are acute events that last for a short time compared to chronic exposure if you live in a city with poor air quality.

The byproducts of burning vegetation, buildings, and other materials include a wide range of harmful substances, including carbon monoxide (CO), carbon dioxide (CO₂), volatile organic compounds (VOCs), and polycyclic aromatic hydrocarbons (PAHs). Wildfire smoke contains large amounts of fine particulate matter (PM2.5), which is small enough to penetrate deep into the lungs and enter the bloodstream. Wildfire smoke also contributes to the formation of ground-level ozone (O₃), which exacerbates the impact on air quality and health.

The Evidence of Exposure to Wildfire Smoke

One study assessed associations between prenatal exposure to wildland fire smoke and risk of preterm birth, which is birth before 37 weeks. In evaluating over 5 million births, researchers found higher wildland fire PM_2.5 exposure was associated with higher odds of preterm birth. For every small increase (1 µg/m³) in wildfire PM_2.5 levels, the risk of preterm birth increases by 1.3%. The risk was highest during the second and third trimesters. Research shows that wildfire PM_2.5 has a stronger effect on pregnancy outcomes than ambient PM_2.5 and increases gestational hypertension and eclampsia risk. Similar to air pollution, evidence shows wildfires are associated with low birth weight.

Limiting Your Risk

While all this sounds scary, let’s keep it in perspective and discuss how to limit your risk. The most obvious way to limit your risk of air pollution or the effects of smoke from wildfires is to avoid exposure in the first place. Unfortunately, that may not be possible if you live in areas affected by these conditions. Let’s focus on what you can control and the steps you can take to limit your exposure.

The Air Quality Index

The Air Quality Index is a tool from the Environmental Protection Agency that rates air quality on a scale of 0-500 based on measurements of pollutants. You can check daily air quality levels in your area with the weather app on your phone. A green range from 0-50 is good with little or no risk. Yellow from 51-100 is a moderate risk for some people, particularly those unusually sensitive to air pollution. Orange from 101-150 is unhealthy for sensitive groups, but the general population is unlikely to be affected. Levels over 150 range from unhealthy to hazardous. If there are days when the air quality is outside of the green range, you may consider limiting your time outside or performing any exercise, especially cardio, indoors. Thankfully, if wildfires affect air quality, it tends to be for a short period of time.

Using Air Filtration

If your home has an HVAC system, you should replace the filter every two months or when it becomes dirty. The higher the filter’s MERV rating, the more particles it can remove from the air. You could consider upgrading your filter to one with a MERV rating of at least 13 or above.

Portable air cleaners or air purifiers remove particulate matter and other pollutants from the air. The most effective types of air cleaners are those with HEPA-rated filters. Portable units are best for single-room use, and large areas and homes may need more than one air cleaner. You can also move a portable air cleaner from one room to another so it is in the room where you spend most of your time. Keeping doors and windows closed in the room where the air purifier runs will increase its effectiveness. You will also need to replace filters periodically.

There is evidence that HEPA or MERV-rated filters can reduce particulate matter and pollutants from wildfire smoke. The downside of air purifiers is cost, especially if you require more than one unit. The American Lung Association has instructions for a DIY air cleaner that requires a box fan and a furnace filter. This could be an inexpensive alternative if a commercial air purifier is out of your budget. Learn more about how to make your own air cleaner here.

Improving Air Quality in Your Home

You can limit other sources of air pollution in your home by using the exhaust fan in your kitchen or opening a window when you cook. You can also reduce the amount of indoor air pollution by eliminating fragrant and scented products like air fresheners and cleaners and using more natural or unscented products. Regular dusting can also improve indoor air quality. While opening windows to get fresh air is beneficial, this may not be an option if you are impacted by wildfire smoke.

Masks

Another intervention to reduce exposure to wildfire smoke is to wear a mask. A cloth or surgical mask is fairly effective at keeping out ash from wildfires but does not filter out smoke well. A respirator mask, like an N95, far outperforms cloth and surgical masks in filtering wildfire smoke. A respirator mask’s efficacy also depends on proper fit and minimizing leakage. It will not filter out 100% of the smoke, but it will significantly reduce your exposure if you are exposed to wildfire smoke.

Antioxidants

One of the mechanisms by which air pollution or wildfire smoke is hazardous to your health is by creating oxidative stress. Oxidative stress occurs when there is an imbalance between the production of harmful molecules called reactive oxygen species and the body’s ability to neutralize them using antioxidants. There is evidence that including antioxidants in your diet could mitigate some of the effects of poor air quality. Common antioxidants include vitamins E, C, A, omega-3s, and selenium. There is also evidence that sufficient vitamin D levels might help counteract the harmful effects of pollution by reducing inflammation.

It is critical to take a high-quality prenatal vitamin that should include these essential antioxidants. If you take a prenatal that does not contain DHA, a powerful omega-3, you may consider taking that as an additional supplement. You can learn more in these episodes on Omega 3 and Fish Oil Supplements During Pregnancy and Ensuring Optimal Vitamin D Levels for You and Your Baby. One of the simplest ways to increase antioxidants in your diet is to include fruits and vegetables in a wide variety of colors. Please talk to your doctor or midwife if you are considering taking additional antioxidant supplements.

Talk to Your Doctor or Midwife

In an ideal world, everyone always had access to clean air free from pollutants or smoke. Many circumstances in our modern world come with risks. While some of these may not be avoidable, you can almost always take action to mitigate your risk and minimize adverse effects. Also, remember that an increased risk doesn’t guarantee you will run into a complication. If you have any questions about your exposure to wildfire smoke or utilizing the interventions discussed in this episode, please discuss it with your doctor or midwife.

Thank you to the amazing companies that have supported this episode.

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