More than 90 percent of pregnant women in a small Indiana study had glyphosate in their urine, and higher concentrations were associated with earlier deliveries.
Glyphosate is the active ingredient in Roundup, the most heavily used herbicide in the United States and worldwide, the study team writes in the journal Environmental Health.
"Glyphosate is often used on major crops on a day-to-day basis . . . but we hardly know anything about how humans are exposed," said lead author Shahid Parvez, a researcher at the Indiana University Fairbanks School of Public Health in Indianapolis.
"We've received an overwhelming response because there's a lot of concern about this chemical," Parvez told Reuters Health in a telephone interview. "We don't want to cause unnecessary panic, but we do want to understand how it affects pregnancy and human health."
Nearly 300 million pounds of Roundup are applied across U.S. farms each year, with the heaviest use in the Midwest, Parvez and his colleagues write.
In 2015 and 2016, the researchers recruited 71 pregnant women in central Indiana and surveyed them about their food and beverage consumption, lifestyle, stress and where they lived. The women also provided two urine samples and two drinking water samples from their homes.
Researchers tested the water and urine for glyphosate and divided women into four groups based on their urine concentration of the chemical. After women gave birth, researchers used medical records to determine their pregnancy length.
Overall, 93 percent of the women had detectable glyphosate in their urine while pregnant. Those who lived in rural areas had higher levels than suburban residents.
Women who drank more than 24 ounces of caffeinated beverages per day also had higher glyphosate concentrations than others. However, none of the drinking water samples had detectable glyphosate.
Pregnancy typically lasts 39-40 weeks; births after 37 weeks are considered full-term. All but two births in this study group were full-term, although researchers found that on average, women with more glyphosate in their urine delivered earlier than women with less or none.
Glyphosate was not associated with other fetal growth indicators such as birth weight or head circumference.
"It was mind-boggling that glyphosate was so prevalent in urine samples . . . but it was a pleasant surprise that none of the drinking water came out positive," Parvez said. "Now we want to learn more about dietary intake and environmental factors such as contaminated air."
The research team was also surprised by the link between caffeine intake and high glyphosate levels in urine.
"It makes sense to us since there are many different food products imported from Southeast Asia and South America but we don't know what they contain," he said. "It indicates a need to think about these food products, such as coffee beans and other drinks that we import."
In addition to its small size, the study is limited by its lack of geographic and racial diversity. More than 94 percent of the women were white, and they came from nine counties that represented a mix of rural, suburban and urban locales, as well as public and well water lines, the authors note.
"Unfortunately, in cases of prenatal exposures, results can take months to years after a child is born to be observable," said Charles Benbrook, a visiting scholar at the Johns Hopkins University School of Public Health in Baltimore who wasn't involved in the study.
Benbrook also works with the Children's Environment Health Network in Washington, D.C., which offers resources on its website for protecting children from chemical exposures (https://bit.ly/2g6oeY2).
In general, Benbrook advised pregnant women to avoid spraying herbicides on the lawn or treating the house for insects when they could be exposed during their first trimester. In addition, he recommended waiting to buy a new car, couch or other home item that could contain chemicals.
"More research needs to be done, but the precautions are common sense," he said. "Be vigilant and careful, especially those living in areas where corn and soybeans are grown."