Can Air Pollutants Increase Your Chances of Miscarriage?
It seems obvious — breathing in toxic air isn’t good for you. (Or for a developing baby.) But did you know that certain air pollutants can affect not only the health of your pregnancy but your ability to get and stay pregnant in the first place?
A growing body of research links air pollution to decreased fertility. A number of studies have shown that toxins in the air can increase the chances of miscarriage as well as giving birth to a preterm or low birth weight baby. Specifically, a new study published in the journal Fertility and Sterility found that short-term exposure to elevated levels of nitrogen dioxide (a pollutant commonly found in traffic) was associated with a 16% increase in miscarriage.
Other studies, such as one published several years ago in the journal Human Reproduction, have similarly shown that increased exposure to nitrogen dioxide is consistently associated with a reduction in the success of IVF outcomes, meaning lower rates of live births.
What do women trying to conceive need to know about air pollution?
In order to dig into this research and to uncover the relevant implications for women trying to conceive, I talked with Dr. Audrey Gaskins, who is a Professor in the Department of Epidemiology at the Rollins School of Public Health at Emory University. Dr. Gaskins has co-authored several studies which highlight the impact that diet and environment may have on fertility.
The main takeaway? Air pollutants can affect the ability of a woman to get and stay pregnant, and many women are not getting this information from their healthcare providers.
Here is the transcript of our interview, which has been edited for clarity.
Q&A with Dr. Audrey Gaskins
What kind of fertility research do you do?
I started working in the field of air pollution and its impact on fertility a couple of years ago when I got a grant from the National Institute of Health, which was mostly focused on spontaneous pregnancies and looking at how air pollution levels are related to early pregnancy loss. And at the time most of the studies had been more ecological—and what I mean by that is that they looked at census-level data showing things like women who live in cities, which tend to have higher air pollution level, have lower fertility rates and things like that.
So while that kind of hinted at an association between air pollution and diminished fertility in women, there were not yet detailed studies looking at this association. So what I proposed to do with this grant was to focus on women undergoing in vitro fertilization. Specifically at the Massachusetts General Hospital Fertility Center, we have an ongoing cohort and we looked at how a woman’s exposure to air pollution in the months leading up to her IVF cycle—as well as during the initial months she’s undergoing treatment—how does that impact her chances of having a pregnancy and eventually giving birth to a live born infant.
The beauty of studying IVF pregnancies is that much of reproduction is externalized. So in addition to very clinical kind of hard end endpoints that patients and providers are very interested in from a research perspective, we could also look at things like embryo quality or egg quality and see if we could determine if air pollution is having a detrimental effect and if so, where. Is the effect on the ovary? Is it on the developing embryo? Is it on the endometrium?
What did you learn about air pollution and IVF outcomes?
So we have one paper that’s been published from this study. It looked very generally at how close a woman lives to a major roadway and its relationship with IVF outcomes. Measuring distance from a major roadway was a way to get at traffic-related air pollution that comes from mostly from traffic. What we saw is that women who live closer to major roadways had higher exposure to traffic-related air pollution had a lower probability of live births following IVF and the effect seemed to be driven by barriers early on in the cycle, meaning that women weren’t responding well to controlled ovarian stimulation. So they were having more cycle cancels or cycles where they would fail early on in terms of fertilization. And then once an embryo transferred, we saw higher odds of pregnancy loss, meaning women who have closer to major railways were more likely to lose that pregnancy, so they were not likely to end in a live birth.
What role does nitrogen dioxide play?
So we’ve now started to look at this question further and instead of using a crude marker for exposure to air pollution, we’ve actually determined the specific levels of different air pollutants for that particular time window—that paper is now under review at a journal, but we presented the results at a meeting this past fall and essentially we’re finding similar results.
So nitrogen dioxide is a primarily a marker of traffic due to the incomplete combustion of fuel and gasoline, and you would expect this pollutant to be higher in the women who are closer to major roadways. And that was the pollutant that was most strongly associated with failing IVF.
In this particular analysis, we saw that the effects of nitrogen dioxide on IVF failure happened early on. We don’t know if this is because the most susceptible women tended to fail early once they were exposed to these high levels of nitrogen dioxide, or if there’s a specific effect of nitrogen dioxide on early oocyte development or hormones—we couldn’t really separate those things in that particular paper.
Does the everyday woman trying to conceive need to limit her exposure to air pollutants?
A source of air pollution that we’re pretty much all exposed to—particularly in urban settings—is traffic. Reducing your exposure to traffic as much as you can is going to be something that environmental health researchers recommend. But there’s only so much you can modify about where you live to reduce your exposure on an individual level. But thinking more broadly, now that we’re starting to focus on these earlier kinds of reproductive points, young people who want to have children someday or at least have the possibility of that can start to be aware that our environment can affect that.
If you changed your lifestyle to reduce your exposure to traffic—would you see a difference immediately?
There have been a number of studies that have come out in the last five years that have tried to analyze this question. One that just came out last week looked at acute changes in exposure to air pollution. It’s one of the unique exposures where on one day—just given the weather conditions and the way the wind’s blowing—you might have really high levels of exposure and then the next day they might be very low. And so we are able to look at short term changes and their effects on pregnancy outcomes. And there have been a couple of studies have shown that when you are acutely exposed to high levels of air pollution, your risk of losing a pregnancy is also increased. So, this seems to suggest that modifications, even on the day level, could be important.
What about drastic changes in air quality from wildfires or other natural disasters?
I’m really interested in that as well because these natural disasters can create a unique setting where we can really look at the impact of certain pollutants. Like in the case of wildfires, the pollutants are very different from those that are a result of traffic. And potentially, we can try to determine if perhaps one pollutant is really harmful, but another one’s not as bad.
I’ve talked with some colleagues in the Bay Area about the possibility of doing research like this and their main concern is always that when these wildfires are going on, the level of stress is also extremely high and so being able to tease out stress versus high levels of pollution will always be challenging.
Are women informed by their doctors about how environmental factors can affect their fertility and pregnancy?
I would say that it’s almost never brought up. There are no guidelines from the American College of Obstetricians & Gynecologists or any of the leading reproductive medicine or OB-GYN organizations relating to environmental exposures. So I would say this is an area where we essentially don’t give women information. So you’d have to find it online or through doing your own research or just hearing it through word of mouth. During initial prenatal visits or annual care visits, it’s very hard to fit in one more topic. But at present, women are really receiving no advice on this.
Historically it was very hard to know the level of air pollution that you’re exposed to, but that’s increasingly changing—you can see the level of air pollution in your area when you look up the weather. So I think as consumers become more informed and the information is more readily available to them, hopefully, more people will understand the impact of air pollution on health and how they might be able to modify their lifestyle to avoid it as much as possible.
What else should women know about diet or the environment when it comes to getting pregnant?
My research has been mostly in diet and how that affects fertility. And I got interested in air pollution because it acts on a lot of the same pathways as diet. One paper that we presented this past fall—and it’s under review now at a journal— looked at the interaction between diet and air pollution. In this case, we looked at high amounts of folic acid, which are in the standard prenatal supplements. We looked to see if that could potentially protect women against the adverse consequences of air pollution exposure. And in fact, we did see that. So among women with high consumption of folic acid, we saw that the effects of air pollution were really muted, meaning that there was no effect. But among women with a lower intake, the effects of air pollution were particularly strong.
It’s hard to modify your air pollution exposure. You can’t really imagine telling people to stay indoors all day every day, but trying to find something that might be a little bit more modifiable at the individual level is an easier public health message to sell to consumers. And it’s interesting because they’ve also shown similar interactions with other environmental chemicals as well.
What other environmental chemicals affect pregnancy?
A great example is this Bisphenol A or BPA. It’s suspected—and almost at this point known—to be an endocrine disrupting chemical. And numerous studies have documented its adverse consequences on female reproductive processes: everything from ovarian reserve to outcomes of infertility treatments. And again, when we looked at how it interacts with folic acid, we saw that it was really among women who are consuming low levels folate that the effects of BPA were particularly pronounced. So, this is a really interesting area of research moving forward because even though we know BPA can be found in things like the lining of cans and other consumer products, it’s actually very challenging to appreciatively reduce your exposure levels.