Exposures to air pollution have been associated with
lower conception and fertility rates. However, the
impact of pollution on infertility incidence is
unknown.
A prospective cohort study used data collected from
116 430 female nurses from September 1989 to
December 2003 as part of the Nurses' Health Study II
cohort.
Infertility was defined by report of attempted
conception for ≥12 months without success.
Participants were able to report if evaluation was
sought and if so, offer multiple clinical
indications for infertility.
After exclusion, 36 294 members were included in the
analysis.
Proximity to major roadways and ambient exposures to
particulate matter less than 10 microns (PM10),
between 2.5 and 10 microns (PM2.5–10), and less than
2.5 microns (PM2.5) were determined for residential
addresses for the 36 294 members between the years
of 1993 and 2003.
Hazard ratios (HR) and 95% confidence intervals (CI)
were calculated using multivariable adjusted Cox
proportional hazard models with time-varying
covariates.
Over 213 416 person-years, there were 2508 incident
reports of infertility. Results for overall
infertility were inconsistent across exposure types.
We observed a small increased risk for those living
closer to compared to farther from a major road,
multivariable adjusted HR = 1.11 (CI: 1.02–1.20).
This was consistent for those reporting primary or
secondary infertility.
When women lived close to major roads, they were 5
percent more likely to report primary infertility,
but these women were 21 percent more likely to
report secondary infertility than women who lived
farther away, and that increase was statistically
significant, researchers report in the journal Human
Reproduction.
In addition, the HR for every 10 µg/m3 increase in
cumulative PM2.5–10 among women with primary
infertility was 1.10, and similarly was 1.10 for
those with secondary infertility.
Within the 2 year window of infertility diagnosis,
we do not have the exact date of diagnosis or the
exact timing of the start of attempting conception.
As infertility status and subtypes of infertility
were prospectively collected biennially, we were
unable to tightly examine the timing of exposures on
incidence of infertility. In terms of exposure
quantification, we used ambient air pollution
exposures as a proxy for personal exposures,
potentially leading to exposure misclassification.
However, several studies suggest that ambient
measurements are an acceptable surrogate for
individual level exposures in most populations.
Researchers observed an association between all size
fractions of PM exposure, as well as traffic-related
air pollution, and incidence of infertility. Of
note, the strongest association was observed between
cumulative average exposures over the course of
follow-up and the risk of infertility, suggesting
that chronic exposures may be of greater importance
than short-term exposures.
For more information
Human reproduction
S. Mahalingaiah, J.E Hart, F. Laden, L.V. Farland,
M.M. Hewlett, J. Chavarro, A. Aschengrau, and S.A
Missmer
Adult air pollution exposure and risk of infertility
in the Nurses' Health Study II
Hum. Reprod. first published online January 2, 2016
doi:10.1093/humrep/dev330
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