Babies' brain development is unlikely to be impaired by exposure to mercury found in contaminated fish while they are still in the womb, research suggests.
Certain types of fish have high mercury levels
There has been widespread concern that mothers who eat certain types of ocean fish may be compromising their baby's development.
This is because some species of fish - including tuna, shark, swordfish and marlin - absorb mercury.
Mercury is found naturally in the environment. It can also occur as a result of pollution.
Exposure to the metal has been linked to damage to the brain and nervous system. It has also been linked to fertility problems.
The UK's Food Standards Agency advised pregnant women earlier this year to limit their consumption of tuna to two medium size cans of tuna a week.
However, a new study published in The Lancet medical journal suggests that women have little to worry about.
A team from the University of Rochester focused on mothers and children in the Seychelles - where fish in the main component of the local diet.
The mothers who took part in the study averaged 12 fish meals a week - compared with just one per week in the US.
A battery of tests on the children found no evidence that their development had been hindered by exposure to mercury.
In an accompanying commentary, Dr Constantine Lyketsos from Johns Hopkins Hospital, Baltimore, says: "On balance, the existing evidence suggests that methyl mercury exposure from fish consumption during pregnancy, of the level seen in most parts of the world, does not have measurable cognitive or behavioural effects in later childhood.
"For now, there is no reason for pregnant women to reduce fish consumption below current levels, which are probably safe."
The World Health Organization is due to discuss the problem of mercury contamination in fish at a meeting next month.
In a statement the FSA said it had been advised by its independent advisory Committee on Toxicity that it should reconsider its opinion on mercury in fish after this meeting.
"Current FSA advice, based on the COT's review of existing scientific knowledge, is for women who are pregnant, planning pregnancy or breastfeeding to avoid eating fish with the highest levels of mercury (shark, swordfish or marlin), and not to eat fish with moderate levels of mercury (tuna) too often.
"The agency will take the conclusions of both the WHO and the COT into account during its review of benefits and risks of fish consumption."