On the one hand, pregnant women are told to eat some oily fish, while on the other hand they are told not to eat so much that the levels of mercury in their bodies rise.
Some oily fish, consumed about twice a week, helps enhance the birth weight and brains of babies, as well as preventing premature births.
Shark, marling and swordfish have the highest levels of mercury and should be avoided by pregnant women, say the researchers.
You can read about this study in the journal Environmental Health Perspectives (EHP).
The researchers studied data on 1,024 pregnant women from Michigan. Their levels of mercury were measured by taking hair samples. It was found that women who gave birth more than two weeks before their expected delivery times were three times as likely to have much higher levels of mercury than women whose mercury levels were within acceptable limits. The researchers also found that the women who had much higher levels of mercury also ate canned, oily fish more often, when compared to women to most women whose mercury levels were normal.
As the study was fairly small - only 44 premature births - further studies are needed, said the scientists.
If you are pregnant and decide to take fish oil supplements, don’t buy the ones that have high levels of vitamin A (retinol), as too much retinol is not good for the developing baby.
“Maternal Fish Consumption, Mercury Levels and Risk of Preterm Delivery” Fei Xue, Claudia Holzman, Mohammad Hossein Rahbar, Kay Trosko, Lawrence Fischer EHP DOI: 10.1289/ehp.9329 Click here to download full article (PDF)