Northern California pregnant women have higher PBDE flame retardant levels than any other pregnant women worldwide, a new study published in Environmental Science & Technology reports. The authors added that they also found evidence that some flame retardants could be undermining thyroid hormone signaling during pregnancy - something which might affect the brain development of the fetus.

The authors say their study is one of the most extensive ones yet on flame retardant exposure in pregnant mothers.

Ami Zota and team explain that chemicals used as flame retardants, known as PBDEs (polybrominated diphenyl ethers), have been used extensively in carpets, consumer electronics, wire insulation, plastics, furniture foam, and several other types of products since the 1970s.

Even though PBDE manufacturing has been banned in the state since 2004, humans are still exposed because of old products, food, house dust and other sources.

According to prior studies, the authors explain, PBDE exposure can mess with the pregnant mother's thyroid function, which may affect the normal development of the fetus' brain, causing lifelong problems. There may also be detrimental consequences for the mother.

The investigators assessed 25 pregnant women from Northern California - they were all in their second trimester. They found they had the "highest-ever levels of certain PBDEs among pregnant women worldwide".

The authors wrote that California's furniture flammability requirements, which manufacturers had to comply with since 1975 by adding PBDEs to upholstered furniture, were probably the cause of the high presence of PBDEs in pregnant women.

The authors concluded in an Abstract in the journal:

"Our results indicate that PBDE exposures are elevated in pregnant women in California, and suggest a relationship with thyroid function. Further investigation is warranted to characterize the risks of PBDE exposures during pregnancy."