Nitrate risk in pregnancy

Women exposed to nitrate in their drinking water during pregnancy are at risk for preterm birth

Photo of a pregnant woman holding a glass of water, by kryzhov/ Shutterstock image

Pregnant women exposed to too much nitrate in their drinking water are at greater risk of giving birth prematurely, according to a study of more than 1.4 million births in California.

Most affected were women whose tap water exceeded the federal nitrate limit of 10 mil-ligrams per liter, double the effect of levels of less than 5 milligrams. But effects were also seen at levels between 5 and 10 milligrams.

“That was surprising,” said lead author Allison Sherris, a graduate student in the Emmett Interdisciplinary Program in Environment and Resources at Stanford. The senior author was Gary Shaw, DrPH, professor of pediatrics.

The largest impact occurred in farming regions, where agricultural runoff leads to higher levels of nitrate in groundwater.

“This is one of many environmental justice issues facing women in rural California,” Sherris said. The research published online May 5 in Environmental Health Perspectives.

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Erin Digitale

Erin Digitale is the pediatrics senior science writer in the Office of Communications. Email her at

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