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 Researchers analyzed pregnancy rates over nine years and more than
6,600 IVF cycles at a Seoul fertility clinic and found reduced
conception rates and increased pregnancy losses among women exposed
to the highest levels of five types of air pollution.
"Although the specific mechanism is unclear, high ambient air
pollution has been suggested to affect processes of conception
assisted by in vitro fertilization (IVF), which means the impact of
air pollution can be profound in couples who are suffering from
infertility," said lead author Dr. Seung-Ah Choe of the School of
Medicine at CHA University and the CHA fertility clinic in Seoul.
Past research has linked high concentrations of air pollutants
produced by combustion of fossil fuels or wood to heart disease,
stroke and inflammation, as well as infertility, the researchers
note in Human Reproduction.
To see if pollution affects the success of fertility treatment, the
researchers examined records for 4,581 women who underwent one or
more IVF cycles from 2006 through 2014. They also used
district-level pollution-monitoring data from 40 sites around the
city to estimate each woman's average hourly exposure during her
fertility treatments to nitrogen dioxide, carbon monoxide, sulfur
dioxide, ozone and tiny pollution particles known as PM 10.
These are major constituents of emissions from traffic vehicles,
construction or industrial sites, Choe said in an email.
The researchers examined the effects of each pollutant at each of
four stages in the IVF process, starting with ovarian stimulation to
retrieve eggs, followed by embryo transfer to the uterus, then a
hormonal test to detect early pregnancy and a later test to confirm
ongoing pregnancy.
The women's average age was 35 and half of them had two or more
embryos transferred over the entire course of their IVF treatments.
Overall, about 51 percent achieved any pregnancy.
Per cycle, there was a 9.4 percent rate of so-called biochemical
pregnancy loss, when the first hormone test indicates a very early
pregnancy, but the subsequent test indicates that it was not
sustained. For later confirmed pregnancies, known as intrauterine
pregnancy, the per-cycle loss rate was 38 percent.
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Researchers found that pollution exposure during the first and third
phases of the IVF process was associated with pregnancy losses.
During the earliest phase, increased exposure, relative to other
women, to nitrogen dioxide and carbon monoxide were tied to
reductions of 7 percent and 6 percent, respectively, in the chances
of attaining intrauterine pregnancy.
During the third phase of IVF, higher exposure to nitrogen dioxide,
carbon monoxide and PM 10 were also associated with 7 percent to 8
percent lower odds of intrauterine pregnancy. Nitrogen dioxide and
PM 10 exposure were also tied to 17 percent and 18 percent,
respectively, higher chances of biochemical pregnancy loss.
"Basically their analyses showed that higher outdoor levels (of
pollution) around the timing of ovarian stimulation and just after
the embryo was transferred back to the mother predicted a failure to
conceive and maintain pregnancy in invitro fertilization (IVF)
patients," Lindsey Darrow, an environmental epidemiologist at Emory
University's Rollins School of Public Health who wasn't involved in
the study, said in an email.
The results are limited by the fact that researchers didn't have
information about other exposures, such as smoking, the study team
notes. And the analysis wasn't a controlled experiment designed to
determine whether or how air pollution might directly affect
fertility.
Even though the mechanism behind the pregnancy loss is unknown, said
Dr. Matthew Peterson of the University of Utah, who wasn't involved
in the study, "those of us who have investigated particle matter and
other pollutants feel that there are negative effects that are
mediated by a number of different pathways (such as) endocrine
disrupting activities such as polyaromatic hydrocarbons, trace
chemical activities or other epigenetic modalities."
For those looking to conceive via IVF, increased awareness can be
helpful, said Darrow, for example, paying attention to the local Air
Quality Index and avoiding going outside when pollutant
concentrations are highest.
"But ultimately there is a limit to how much individuals can control
their own air pollution exposures. Outdoor air pollution is one of
those problems we can only really address through collective
action," she said.
SOURCE: https://bit.ly/2Fkyc1U Human Reproduction, online April 5,
2018.
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