The short answer
NHS lists cooked shellfish as safe to eat in pregnancy, and names them: prawns, crab, lobster, squid, mussels, scallops, clams and cockles. Sushi made with cooked fish or cooked shellfish is on the same safe list.
The advice to avoid applies to raw shellfish, which NHS says can contain bacteria or toxins that can make you seriously unwell or give you food poisoning.
So a cooked prawn sandwich, mussels in a broth, or a crab salad made with cooked crab are not the situations the warning is about. Raw oysters are.
Why shellfish concentrates what is in the water
Bivalves such as oysters, mussels, clams and scallops feed by filtering large volumes of seawater and retaining what is suspended in it. That is an efficient way to eat, and an efficient way to accumulate whatever the surrounding water contains.
It is the reason shellfish appears in food-safety guidance more often than its share of the diet would suggest, and the reason the cooked-versus-raw line matters more here than for most foods. Cooking deals with bacteria and viruses. Eating them raw skips the only step that does.
The part cooking does not reach
This is the genuinely surprising bit, and it belongs on the same shelf as the vitamin A point in the pâté and cured meat guide: not every food risk is a germ, and the ones that are not do not respond to heat.
The Canadian Food Inspection Agency is explicit that cooking bivalve shellfish does not destroy the toxins that cause paralytic, amnesic and diarrhetic shellfish poisoning, and that properly cooked shellfish can still be toxic. These marine biotoxins come from algae the shellfish have filtered, and they are stable in a way bacteria are not.
Read that carefully rather than alarmingly, because the next paragraph is the one that matters.
Why that is not a reason to avoid cooked shellfish
Biotoxins are managed before shellfish reaches a shop, not by the person eating it. Monitoring programmes test harvesting areas and close them when toxin levels rise, which is why commercially sold shellfish is not where this risk usually sits.
Where it does sit is shellfish gathered privately from a beach, or eaten in defiance of a local harvesting advisory. So the practical translation for pregnancy is short: buy from reputable commercial sources, and do not collect your own shellfish while you are pregnant, however tempting the tide is.
That is the whole reason the biotoxin point is worth explaining rather than hiding. Without it, a well-meaning "just cook it thoroughly" sounds like a universal rule, and it is not one.
Sorting the common situations
| Situation | Where NHS guidance puts it |
|---|---|
| Cooked prawns, crab, lobster, squid, mussels, scallops, clams, cockles | Safe to eat |
| Sushi made with cooked fish or cooked shellfish | Safe to eat |
| Raw oysters, raw clams, ceviche, and other raw shellfish | Avoid, because of bacteria or toxins |
| Shellfish you gathered yourself | Not a cooking question. Monitoring and local advisories are what manage biotoxins, so this is the situation to skip during pregnancy. |
| Cold cooked seafood from a counter or buffet | Cooked, so the raw-shellfish rule does not apply, but it is a chilled ready-to-eat food. Storage and use-by dates matter the same way they do for other cold counters. |
Categories from NHS guidance on foods to avoid in pregnancy, with biotoxin handling from the Canadian Food Inspection Agency fact sheet on shellfish toxins.
Mercury is a separate question again
Shellfish is not where the mercury conversation lives. That one is about fish species and weekly servings, and it is covered in the tuna guide. Keeping the two apart matters, because someone worried about mercury does not need to avoid prawns, and someone worried about raw oysters is not solving it by choosing a lower-mercury option.
If you already ate raw shellfish
One oyster is not proof that anything went wrong, and this is a common thing to eat before remembering the advice.
For the bacterial and viral side, the clock is short rather than long. This is not the ten-week Listeria window that applies to soft cheese; the illnesses associated with raw shellfish generally announce themselves within hours to a few days, usually as stomach cramps, vomiting, diarrhoea, or fever.
Shellfish poisoning from biotoxins is different again and can begin quickly, sometimes with tingling or numbness around the mouth rather than only stomach symptoms. That combination is a reason to seek urgent medical advice rather than to wait and see, and it is worth mentioning that you ate shellfish when you do.
Otherwise, note what you ate, where it came from, whether it was raw or cooked, and when, then contact your doctor, midwife or maternity service if you feel unwell or want advice for your own situation. The food poisoning guide covers symptoms, hydration, and how to write the message.
Keep the source with the meal
For shellfish the useful details are unusually specific: raw or cooked, where it came from, and whether it was commercially bought. Nouri can hold those with the date so a later question has something behind it.
Common questions
Can you eat prawns while pregnant?
Yes, when they are cooked. NHS lists cooked shellfish, including prawns, crab, lobster, squid, mussels, scallops, clams and cockles, under foods that are safe to eat in pregnancy. The advice to avoid applies to raw shellfish.
Why is raw shellfish different?
NHS says to avoid raw shellfish because it can contain bacteria or toxins that can make you seriously unwell or give you food poisoning. Shellfish filter large volumes of water, so anything in that water concentrates in them. Cooking deals with the bacteria and viruses; eating them raw skips that step.
Are oysters safe if they are cooked?
Cooked shellfish is on the NHS safe-to-eat list, and that includes oysters cooked through. The reason oysters get singled out in food-safety advice is that they are usually eaten raw, not that the animal is uniquely dangerous once cooked.
Does cooking destroy shellfish toxins?
No, and this is the one part worth knowing. The Canadian Food Inspection Agency says cooking bivalve shellfish does not destroy the toxins that cause paralytic, amnesic and diarrhetic shellfish poisoning, and that properly cooked shellfish can still be toxic. These marine biotoxins are a different category from bacteria.
Does that mean cooked shellfish is unsafe?
No. Biotoxins are managed before the shellfish reaches you, through monitoring programmes that close harvesting areas when toxin levels rise. The practical consumer advice is to buy from reputable commercial sources and to heed local shellfish harvesting advisories rather than gathering your own, which is where the real exposure risk sits.
Related Nouri pages
Sources checked on 1 September 2026
- NHS: Foods to avoid in pregnancy, fish and seafood section
- Canadian Food Inspection Agency: Marine biotoxins in bivalve shellfish
- CDC: Safer food choices for pregnant women
- CDC: Symptoms of Listeria infection, for comparison of timings
Open the linked source for its latest version. This page is educational and does not decide whether a specific meal was safe for you.