Pregnant women who eat fish more than three times a week could be putting their baby at risk because of higher mercury levels in their blood, according to a study by Taiwanese researchers.

Mercury exposure is especially risky for fetuses when their internal organs are developing, and can result in neuronal, kidney, and brain damage, and can stunt growth.

Expectant Chinese mothers tend to eat more fish as they believe it is healthier than red or white meat.

A study of 65 pregnant women in Taipei found mercury concentrations of around 9.1 micrograms per liter in their blood and around 10 micrograms per liter in blood in their umbilical cords. The researchers also found an average of 19 nanograms per gram of mercury in their placenta.

Such levels were way over what are considered safe, the researchers wrote in a paper to be published in January in the International Journal of Obstetrics and Gynecology.

Eighty-nine percent had blood mercury concentrations exceeding the U.S. National Research Council’s recommended value of 5.8 micrograms per liter.

The women were recruited for the study 24 weeks into their pregnancy.

"When a woman consumes fish, it is absorbed in the gastrointestinal tract and enters the bloodstream. The trace elements of mercury, or methylmercury, the commonly found form of mercury in fish, passes through the placenta and then to the fetus," the researchers said.

The U.S. Food and Drug Administration advises pregnant women to avoid eating fish with high mercury levels such as shark, swordfish, king mackerel, and tilefish.

Instead, it recommends fish and shellfish that are lower in mercury, such as shrimp and tilapia.

Via Reuters