A new study suggests that despite concerns of exposure to mercury, pregnant women that eat a lot of fish may not harm their unborn child.  In fact, it could help prevent fetuses from having developmental issues later, as has been previously believed.

All fish contain trace amounts of the element mercury, a substance known to harm unborn children and which can cause developmental issues later in their lives.  So for many years now, doctors have been advising women who enjoyed a diet rich in fish or shellfish to keep it down to a minimum while they were pregnant.

After three decades of research in the Seychelles Islands of the Indian Ocean, scientists found no developmental problems in children born to women who consume fish at a much higher rate than the average American woman.

"They eat a lot of fish, historically about 12 fish meals a week, and their mercury exposure from fish is about 10 times higher than that of average Americans," says study coauthor Edwin van Wijngaarden, an associate professor in the University of Rochester's department of Public Health Sciences. "We have not found any association between these exposures to mercury and developmental outcomes."

According to the study, the omega-3 fatty acids found in fish oil may actually protect the brain from the toxic effects of mercury and other potential substances that are toxic to unborn fetuses. The researchers only found mercury-related developmental problems in children of women who had low omega-3 levels, but high levels of omega-6 fatty acids.

"The fish oil is tripping up the mercury," van Wijngaarden says. "Somehow, they are interacting with each other. We found benefits of omega 3s on language development and communications skills."

Currently, the U.S. Food and Drug Administration recommends pregnant women only consume fish twice a week at most.  However, in June 2014 the FDA announced that it plans to update recommendations and advise pregnant women to eat a minimum of two to three servings of fish known to be low in mercury per week.

"It's not clear that the current recommendation of limiting your fish intake is actually warranted, based on the current data," medical director of labor and delivery at Massachusetts General Hospital in Boston, Dr. Laura Riley says. "This study is again raising that same question. Is this really that bad? Do you need to take into consideration the beneficial effects of eating fish?"

However, Riley isn't convinced that fish oil might protect against mercury. "More study needs to be done before you can convince me that the fish is actually protective," Riley says. "I want to see the data."

The new data suggests that the oil in fish might actually counteract the damage to unborn children before it can occur. 

"The theory is that mercury exposure confers toxicity because it induces oxidation in the human body, which often results in inflammation," van Wijngaarden says. "These omega 3s are more anti-inflammatory. The idea would be that they would reduce the level of inflammation in the mother, softening any effect that mercury might have on the unborn child."

Riley says that pregnant women should continue to avoid fish known to have high levels of mercury, including shark, swordfish and king mackerel. But, she also says that the takeaway message from this study is simple: "Go ahead and eat fish."