The probability of implantation and live birth after in vitro fertilization (IVF) is lower for women who live close to a major roadway, and are therefore exposed to traffic-related air pollution, new research shows.
“Over the past decade, chronic exposure to traffic-related air pollution has become increasingly recognized as an important risk factor for adverse pregnancy outcomes, including preterm birth, gestational diabetes, preeclampsia, restricted fetal growth, and low birth weight,” said Audrey Gaskins, ScD, from the Harvard T.H. Chan School of Public Health in Boston.
The biologic mechanisms that mediate the “effect of air pollution on later pregnancy and birth outcomes — such as increased oxidative stress, systemic inflammation, endothelial dysfunction, and DNA damage — could also affect earlier pregnancy outcomes, such as fertilization, early embryo development, and implantation,” she explained at the American Society for Reproductive Medicine (ASRM) 2017 Scientific Congress in San Antonio.
“However, limited research has been conducted in this regard,” she told Medscape Medical News.
Dr Gaskins and her colleagues assessed 441 women enrolled in the Environment and Reproductive Health (EARTH) study who underwent a total of 670 IVF cycles from 2004 to 2016.
After factors such as maternal age, body mass index, and smoking were controlled for, the researchers found that the probability of live birth after IVF was lower in women who lived close to a class A roadway, defined as an interstate, federal highway, or state highway.
Table. IVF Cycles Resulting in Live Births (Adjusted Percentage)
| Distance of Residence From Major Roadway | Live Births, % | 95% Confidence Interval |
|---|---|---|
| ≤200 meters | 33 | 27–40 |
| ≥1000 meters | 47 | 38–57 |
There was no association between proximity to a major roadway and implantation or clinical pregnancy, but the odds of pregnancy loss was 2.72 (95% confidence interval, 1.24 – 5.96) times higher for women living within 200 meters of a major roadway than for those living more than 1000 meters away.
“We found no associations between our proxies for traffic-related air pollution and oocyte yield or fertilization, but saw probable effects on peak estradiol and endometrial thickness levels, suggesting that the adverse effects we observed related to distance from roadways on implantation could be potentially mediated by hormonal changes that affect the endometrium,” said Dr Gaskins.
“A handful of animal and laboratory studies suggest that impaired embryo development, altered placental function, and abnormal gene expression — all parameters we were unable to assess — could also be plausible mechanisms linking traffic-related air pollution to a lower probability of implantation and live birth,” she reported.
As the number of women seeking medical treatment for infertility continues to rise, a better understanding of the impact environmental factors have on IVF outcomes remains an important health issue, particularly given the high costs and psychologic toll of multiple IVF treatments, she added.
“Our research not only corroborates evidence from studies of women attempting to conceive naturally and through assisted reproduction, it also highlights the fact that exposure to traffic-related air pollution may have an effect on early implantation failure,” Dr Gaskins said. However, “more research is needed to evaluate which specific traffic-related air pollutants are responsible for this association, and whether there is a specific window of heightened susceptibility to the adverse effects.”
“This is an important and intriguing study,” ASRM President-Elect Christos Coutifaris, MD, PhD, chief of the division of reproductive endocrinology and infertility at the University of Pennsylvania in Philadelphia, said in a statement. “Although not surprising, it reinforces that environmental factors play important roles in health and reproduction.”
The study is intriguing, agreed Kevin Doody, MD, director of CARE Fertility in Bedford, Texas, who is immediate past president of the Society for Assisted Reproductive Technology (SART).
But the patient population was small, he pointed out, and there was no light shed on other factors that might have affected IVF outcomes.
“In this type of study, there may be confounding variables,” he explained. “Are the people who live closer to major roadways in a different socioeconomic class? Other factors might come into play.”
“It’s an interesting study, but I think it needs more follow-up and replication, and perhaps larger numbers,” Dr Doody said.
The study was supported by grants from the National Institutes of Health, the National Institute of Environmental Health Sciences (NIEHS), the Eunice Kennedy Shriver National Institute of Child Health (NICHD), and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Dr Gaskins, Dr Coutifaris, and Dr Doody have disclosed no relevant financial relationships.
American Society for Reproductive Medicine (ASRM) 2017 Scientific Congress: Abstract O-91. Presented October 31, 2017.
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