Flame-retardant chemicals that are present in many household consumer products may reduce fertility in women, University of California-Berkeley researchers reported Tuesday.

The study links each 10-fold increase in the blood concentration of four PBDE (polybrominated diphenyl ethers) chemicals to a 30% decrease in the odds of becoming pregnant each month.

These chemicals are used in foam furniture, electronics, fabrics, carpets, plastics and other items. They became common decades ago in the United States when fire safety standards were adopted. They are being phased out nationwide but some are still found in products made before 2004.

The research joins other animal and human studies that show health effects from PBDE exposure and that 97% of U.S. residents have detectable levels of the chemicals in their blood.

"This latest paper is the first to address the impact on human fertility, and the results are surprisingly strong," says lead author Kim Harley, associate director of the Center for Children's Environmental Health Research at the University of California-Berkeley's School of Public Health.

Harley says the chemicals leach into our environment. She says Californians have particularly high levels of PBDEs, most likely because of the state's relatively strict flammability laws.

Even though the chemicals are being phased out, Harley remains concerned. "We know even less about the newer flame retardant chemicals that are coming out," she says in a university press release. "We just don't have the human studies yet to show that they are safe."

In the study, published Tuesday in the journal Environmental Health Perspectives, Harley and other researchers measured PBDE levels in blood samples from 223 pregnant women, many of them young Mexican immigrants in an agricultural community. Their analysis takes into consideration exposure to pesticides and other factors that could affect fertility.

The study says it's not entirely clear how PBDEs impact fertility. Animal studies have found that the chemicals can impair neurodevelopment, reduce thyroid hormones and alter levels of sex hormones.