Mothers-to-be are currently warned to limit their fish intake due to the negative effects of mercury on foetal development.
But scientists say these guidelines may need to be reviewed following a study by the University of Bristol.
The research suggests fish accounts for just 7% of mercury levels in the human body, with all food and drink totalling less than 17%.
Surprisingly, it also found herbal teas and alcohol to be the foodstuffs associated with the highest mercury blood levels, after white and oily fish. Food including French fries, white bread and milk were found to have a protective effect.
Professor Jean Golding OBE, lead author of the report published in Environmental Health Perspectives, said eating fish had health benefits, adding:"We have previously found that eating fish during pregnancy has many health benefits for both mother and child. We hope many more women will now consider eating more fish during pregnancy."
The study involved 4484 women taking part in the Children of the 90s study.
Results showed that 38 of the women, less than 1%, had mercury levels higher than the maximum recommended by the US National Research Council. There is no official safe level in the UK. Women with the highest mercury tended to be older, have attended university, to be in a professional job, own their home and be expecting their first child.
Researchers found food and drink items accounted for less than 17% of total mercury levels in the body.
The levels were most associated with oily fish, white fish, herbal tea, alcohol, boiled rice, fresh fruit, sunflower or other oils used for frying and pasta. Other foods included fruit juice, health foods, brown or granary bread, pulses, shellfish, bran cereals and salad.
Negative predictors of mercury included white bread and French fries.