New Pregnancy Risks: Smog and Heat

Just when you thought there was nothing more to worry about, two new studies reveal two new concerns: smog may increase the chance of a miscarriage and global warming may be associated with a higher risk of premature births, stillbirths, or other negative pregnancy outcomes.

# 1: Smog might raise a woman’s risk of miscarriage early in her pregnancy, a new study suggests. Chronic exposure seemed to increase that risk by more than 10 percent, according to researchers who tracked hundreds of pregnancies among couples in Michigan and Texas. “We found that both ozone and particles in the air were related to an increased risk of early pregnancy loss,” said senior researcher Pauline Mendola. She is an investigator with the U.S. National Institute of Child Health and Human Development.

Mendola and her team reviewed data from a long-term study from the U.S. National Institutes of Health that followed 501 couples between 2005 and 2009. he findings showed that exposure to ozone appeared to increase risk of pregnancy loss by 12 percent, and exposure to fine airborne particles raised it by 13 percent. That was even after the researchers compensated for other factors that can affect the health of a pregnancy, such as age, race, education, income, weight, fertility, and caffeine and multivitamin intake. “When you have air-quality alerts, we would say it’s probably prudent to suggest that pregnant women adapt their behavior,” Mendola said. “Avoid outdoor activities, the same as people with asthma or respiratory disease would.”

# 2: Global warming may be associated with a higher risk of premature births, stillbirths, or other negative pregnancy outcomes. According to an article in the Atlantic, handful of researchers in the United States, Canada, and elsewhere are methodically accumulating evidence suggesting that higher temperatures could be linked to a higher risk of premature births, stillbirths, or other negative pregnancy outcomes. The findings in each case, while compelling, still raise as many questions as they seem to answer, and all the researchers say that much more work needs to be done. But they also suggest that enough evidence has already surfaced to warrant increased scrutiny—particularly as global warming is expected to drive average temperatures ever upward over coming decades.

Research suggests that an increase of 10 degrees Fahrenheit in weekly average “apparent” temperatures—a combination of heat and humidity—corresponded to an 8.6 percent increase in premature births. That association was independent of air pollution. In an analysis of more than 8,500 stillbirths that occurred during a decade of California’s warm seasons: Stillbirth risk was 10.4 percent higher with a 10-degree Fahrenheit apparent-temperature increase.

There is not much one can do to avoid these risks except be prudent when there are high levels of smog or very high temperatures.

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