ECHO Study Suggests Air Pollution, Secondhand Smoke, Formaldehyde Exposure Affect Length of Time to Get Pregnant

Author(s): Eva Siegel, Linda Kahn, et al.

Who sponsored this study?

This research was supported by the Environmental influences on Child Health Outcomes (ECHO) program, the Office of the Director, the National Institutes of Health, with co-funding from the Office of Behavioral and Social Sciences Research (OBSSR).

What were the study results?

The strongest evidence points to an association between exposures to traffic-related air pollution, secondhand smoke, and a chemical called formaldehyde—a common workplace exposure in construction sites and nail salons—and longer time to pregnancy. Specifically, exposure to particulate matter and nitrogen oxide gases lowered couples’ chances of becoming pregnant. Traffic and the burning of other types of materials besides gas and diesel create particulate matter and nitrogen oxide gases. Volatile organic compounds, which are used in manufacturing processes, did not appear to affect time to pregnancy.

What was the study's impact?

This review suggests that certain chemicals in the air may lengthen the time it takes for couples to become pregnant. More research is needed to better understand how these chemicals affect reproductive health. To collect this information, future studies can provide participants with personal air monitors that can let researchers know about the quality of air participants are actually breathing instead of relying on imprecise data from outdoor monitors or participant recall.

The research team also pointed out that there are remaining questions about whether the air people breathe around the time of conception is what matters most or whether there are certain life stages, such as puberty, when being exposed to air pollution may be especially damaging. The ECHO-wide Cohort, which allows researchers to access information from a large and diverse population, can serve as an important resource for answering these questions.

Why was this study needed?

Previous studies have looked at how air pollution may affect how long it takes to become pregnant. Time to pregnancy is a measure used to estimate a couple’s ability to conceive and is commonly used to diagnose infertility. In this paper, the authors review past studies on air pollution to identify types of air pollutants—including pollution from traffic, chemicals in the workplace, and secondhand smoke—that might affect how long it takes to get pregnant.

Who was involved?

This review includes all papers published in English on this topic from January 1, 1990 to February 11, 2021. The analysis covered 33 articles, of which eight looked at outdoor air quality, six looked at secondhand smoke exposure, and 19 looked at air quality in the workplace.

What happened during the study?

The research team searched six leading science libraries and identified 33 human studies related to exposure to outdoor and indoor air pollutants and time to pregnancy. The team read each article, assigned it a score based on the quality of the study design, and created summary tables containing the most important findings of each study. They then compared the consistency of results between studies, especially among high-quality papers, about whether certain types of air pollution affected time to pregnancy.

What happens next?

This is the third review this team of authors has written on chemicals and time to pregnancy. Individual authors will continue to fill in the research gaps previously mentioned, including conducting studies where women will be wearing personal air monitors.

Where can I learn more?

Access the full journal article, titled “Indoor and outdoor air pollution and couple fecundability: a systematic review” in Human Reproduction Update.

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

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Published July 27, 2022