Women exposed to high levels of air pollution may have less success getting pregnant with fertility treatments or staying pregnant, compared to women breathing cleaner air, a South Korean study suggests.
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.
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.