Risk in the womb?

A group of chemicals is associated with miscarriages.

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Between ten and twenty percent of confirmed pregnancies end in miscarriage. While doctors are often hard-pressed to explain the biological reasons behind this heartbreaking statistic, a growing body of research has suggested that perhaps a quarter of all miscarriages have at least one known risk factor. Yale School of Public Health epidemiologist Zeyan Liew and his colleagues have zeroed in on one potential culprit: a group of widely used artificial chemicals known as PFAS, shorthand for per- and polyfluoroalkyl substances.

“PFAS are found just about everywhere,” says Liew. “They’re used in nonstick cookware, food packaging, clothing, all sorts of industrial processes. And, increasingly, they’re in drinking water.”

The various PFAS varieties are also almost ubiquitous in our bodies—where they’re so long-lasting that they’ve been dubbed “forever chemicals.”

Using data from the comprehensive Danish National Birth Cohort (DNBC), a long-running study that now includes more than 100,000 women, the researchers compared 220 women who miscarried in their second trimester with a matched sample who carried to term. The DNBC includes maternal blood sampling, and Liew’s team found that women with the highest PFAS blood levels were about twice as likely to miscarry as women with the lowest levels. (The study appears in Environmental Health Perspectives.)

Association is not causation, Liew notes. But he says the data also show that higher PFAS levels often correlate with lower birth weights, smaller size, immune system suppression, and, in boys, an increase in cerebral palsy. Chemical companies have voluntarily stopped making some of the more common PFAS varieties in the United States, but they still enter the country via imported products. Liew advocates a “precautionary approach: I don’t want to worry mothers-to-be, but I’d advise that they find ways to prevent exposure.

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