Researchers studied about 2,000 mothers and their children, starting from the mothers' first trimester of pregnancy, and continuing until the children turned 5.
Results showed that children whose mothers ate an average of three to four servings during their pregnancy showed no signs that mercury in fish negatively affected their developmental health.
These children had IQ scores that were 2.8 per cent higher than those whose mothers ate less fish, the study found.
For the study, researchers took blood from the babies' umbilical cords after they were born, and measured the levels of both mercury and docosahexaenoic acid (DHA) in their blood, 'Live Science' reported.
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When the children were 14 months old, and again when they were 5, the researchers tested the children to assess their cognitive development and to look for signs of autism spectrum disorder (ASD).
High levels of DHA may outweigh any negative effects of mercury, researchers said.
"Fish such as tuna that may have mercury also hold higher levels of DHA, an omega-3 fatty acid that plays a critical role in brain growth and development," said Julvez.
"Maybe this effect is masking the negative effects that come from mercury. Or, maybe this is more beneficial than the toxic effect of the mercury itself," Julvez said.
The findings were published in The American Journal of Epidemiology.