Is fish safe during pregnancy?

The verdict

Yes. Fish is one of the few foods pregnancy guidance actively tells you to eat more of, not less. The FDA states that fish intake during pregnancy is recommended because moderate scientific evidence shows it can help your baby's cognitive development, and that fish provide omega-3 DHA and EPA, iron, iodine and choline - choline also supporting development of the baby's spinal cord.

The caveats are about species, not about fish. Avoid the high-mercury predators, cook it, and keep to the published limits on tuna and oily fish.

Why mercury, and why these species

The concern is methylmercury, an organic form of mercury that accumulates in aquatic food chains. Long-lived predatory fish at the top of those chains carry the highest concentrations, which is why the avoid lists are species lists rather than quantity limits.

Methylmercury crosses the placenta and is neurotoxic to the developing brain. The FDA puts it plainly: mercury can be harmful to the brain and nervous system if a person is exposed to too much of it over time. Critically, it adds that mercury is found throughout the tissue in fish, so cleaning or cooking will not reduce the amount of mercury. This is not a food hygiene problem and no preparation method helps.

There is a second, separate hazard for oily fish, which is why the NHS caps salmon and mackerel despite them being low in mercury. Oily fish can accumulate pollutants including dioxins and PCBs in their fat. That is the reason for the two-portions-a-week limit, and it is a different mechanism from the mercury rule.

And a third, unrelated to contaminants: raw and cold-smoked fish carry a listeria risk. See our page on sushi and raw fish for that.

How much, and of what

The consensus core

Two to three portions a week of lower-mercury fish, with one of them oily, is the shared recommendation. The NHS says a healthy balanced diet should include at least two portions of fish a week including one of oily fish, and puts a portion at around 140g. The FDA and EPA recommend that those who are pregnant or breastfeeding consume between 8 and 12 ounces per week of a variety of seafood lower in mercury, with a serving at 4 ounces. ACOG says two or three servings of fish or shellfish per week, a serving being 4oz. FSANZ says two to three serves a week.

Avoided everywhere

Shark, swordfish and marlin. Every jurisdiction lists all three.

Avoided in some places only

The FDA's Choices to Avoid list adds four more: king mackerel, orange roughy, tilefish from the Gulf of Mexico, and bigeye tuna. None of these four appears on the NHS avoid list at all.

The mackerel case is the sharpest illustration that the two systems are not describing the same fish. The NHS lists mackerel as a recommended oily fish. The FDA lists king mackerel as a Choice to Avoid with the highest mercury levels, while separately listing Atlantic mackerel and Pacific chub mackerel as Best Choices. These are different species with the same word in the name.

Tuna, where the numbers diverge most

The NHS: no more than 4 cans or 2 tuna steaks a week, based on a medium can with a drained weight of around 140g and a 140g cooked steak. That is up to around 560g of tuna a week, with no distinction between tuna types. Tuna does not count towards the oily fish limit.

ACOG: limit white (albacore) tuna to only 6 oz a week - about 170g.

The FDA splits tuna three ways: canned light tuna including skipjack is a Best Choice at 2 to 3 servings a week; albacore, white and yellowfin tuna are Good Choices at 1 serving a week; bigeye tuna is a Choice to Avoid entirely.

Health Canada is different again: canned albacore (white) tuna is limited to 300g a week for people who are or may become pregnant, while fresh or frozen tuna falls under its high-mercury rule of 150g a month. Canned light tuna is not restricted.

So a UK reader following the NHS may eat over three times as much albacore as an American reader following ACOG, and a Canadian reader may eat fresh tuna at a small fraction of the rate permitted for the canned product.

If you have already eaten a fish on the avoid list

One meal is not the concern. Methylmercury accumulates over months - its biological half-life in the body is measured in weeks - so the guidance is about sustained intake, not a single exposure. No health service tests or treats on the basis of one high-mercury meal, and there is no intervention that would help if it did.

The proportionate response is to skip fish for the rest of that week and go back to the lower-mercury species after that. The FDA uses exactly this logic for fish caught by family and friends where no advisory exists: eat only one serving and no other fish that week.

If you have been eating swordfish or shark regularly over months, mention it at your next antenatal appointment. It is worth having on the record, though there is unlikely to be any action beyond stopping.

Do not respond by cutting out fish. Both the FDA and the NHS are explicit that the nutritional benefit of fish in pregnancy is real and that under-eating fish has its own cost.

Where guidance genuinely differs

This is the food where national lists diverge most, and the divergence is structural rather than a disagreement about the science.

The FDA publishes a 62-species chart. The NHS names three fish. The FDA and EPA sort 62 types of fish into Best Choices, Good Choices and Choices to Avoid. The NHS gives an avoid list of shark, swordfish and marlin, plus limits on tuna and oily fish. Neither is wrong; they are different regulatory traditions, and a reader moving between them will find species that are addressed in one country and simply absent in the other.

Australia counts in fortnights. FSANZ's mercury guidance for people who are pregnant or planning pregnancy is 1 portion per fortnight of shark (flake) or billfish (swordfish, broadbill and marlin) and no other fish that fortnight, or 1 portion per week of orange roughy (deep sea perch) or catfish and no other fish that week. A portion is 150g. Note that this permits shark, which the UK and US rule out entirely - at a controlled frequency. FSANZ has also removed the number for all other fish from its mercury table, noting that the 2 to 3 serves figure reflects dietary guidelines rather than safe-consumption guidance.

Canada counts in months. Health Canada limits fresh or frozen tuna, shark, swordfish, marlin, orange roughy and escolar to 150g per month for people who are or may become pregnant, against 150g per week for the general population. Escolar appears on no other country's list. Canned albacore is handled separately at 300g a week.

The oily fish cap is largely a UK rule. The NHS limits oily fish - herring, pilchards, salmon, sardines, sprats, trout and mackerel - to two portions a week for anyone who could become pregnant, on pollutant rather than mercury grounds. The FDA has no equivalent cap: salmon, sardines, herring and Atlantic mackerel are all Best Choices at 2 to 3 servings a week, and the FDA's advice is framed around eating more of them, not fewer.

If you want a single rule that works everywhere: two to three 140g portions a week of salmon, sardines, cod, haddock, prawns or canned light tuna, no shark, swordfish, marlin, orange roughy or king mackerel, and no more than one portion a week of albacore tuna.