Fish is good for you, it’s rich in omega-3, vitamin D and other nutrients, and there is evidence that eating oily fish in pregnancy may be beneficial to the unborn baby. However, there are also risks to be aware of when eating fish.
Here a run-down of things you should be aware of when eating fish and seafood in pregnancy:
Mercury is a neurotoxin. It’s not good for you in high concentrations, and foetuses, babies and young children are most susceptible (a detailed description of the problems it ,any cause can be found here, page 16). Though its naturally present in the environment, levels have increased due to human activity. When mercury leaches into the water it turns to methylmercury, and accumulates in fish.
Mercury can accumulate up the food chain. A swordfish, for example, will consume a huge quantity of smaller fish in its nine year lifespan. When it eats a fish that is contaminated with mercury, that mercury passes to the swordfish will therefore have a far higher concentration of mercury than the smaller fish.
Marlin, shark, swordfish and tuna are large fish at the top of the food chain with relatively long lifespans. The NHS recommends avoiding the consumption of marlin, shark and swordfish and limiting tuna consumption to two tuna steaks or four cans of tuna a week (which seems quite a lot to me!)
The safe level of mercury consumption is debatable. The current level suggested by the Codex Joint Expert Committee on Food Additives is 1.6 micrograms per week per kilogram of body weight. This is a conservative estimate of the level to stay under to avoid damage to a foetus. The report suggests that a concentration two times higher than this would not cause neurotoxicity in adults.
So for a 60kg pregant woman (I wish), that’d be 96micrograms per week (the red line on the chart below). Let’s look at the fish then. According to the US Food and Drug Administration fish muscle surveys:
*this is the upper limit of a range. Note, there are also some more unusual fish that contain above the recommended levels of mercury, but they aren’t regularly available on the UK. They’re listed in the original table of you’re interested. Also, tuna is a very varied fish, in terms of size and therefore in terms of mercury concentrations. I’ve just checked the cans in my cupboard – they’re yellowfin. Most canned tuna is skipjack or yellowfin, which are quite low in mercury.
Oily fish (including tuna steak, but excluding canned tuna) can also be a source of pollutants; dioxins and polychlorinated biphenyls are the main concern. In high doses these can cause wide ranging problems, including cancer, gastrointestinal and respiratory problems, and affects on the immune system and reproductive system (lots of detail here). A limit of 70picograms per kg of body weight per month has been set, and it is estimated that the majority of the population consumes far fewer of these pollutants. To be sure, the NHS recommends pregnant women eat no more than two 140g portions of oily fish a week. The NHS site defines which fish are included in this.
See my Listeria page for an in-depth look at avoiding Listeria in pregnancy. As I’ve mentioned previously, the NHS guidelines state that smoked salmon is safe to eat in pregnancy. However, other countries say to avoid it, and Listeria has been isolated from smoked fish. Cold prawns, bought precooked, are also a potential risk, albeit quite low, as are fish pâté and tarama/taramasalata.
Because the environment shellfish live in can easily be contaminated with pathogens, they are a particular risk for food poisoning. The NHS guidelines are that you should avoid raw shellfish while pregnant. The majority of pathogens will be killed during cooking (some rare toxins are not), so cooked shellfish is much less of a risk. Fish are less likely to be a cause of food poisoning, and raw fish is no more risky than other raw food.
Fish may contain a parasite called anisakis. The parasite can infect humans, causing nausea, vomiting and abdominal pain. Cooking, curing or freezing can kill the parasite. Raw sushi is generally fine to eat in pregnancy, provided any wild fish has been frozen first. This is common practice in most shops and restaurants.
What did I do?
The NHS guidelines seem quite robust in regards to fish. The only thing I did differently was to avoid smoked fish and cold cooked prawns, as I felt the risk of Listeria, however low, was just not worth it.
The mercury and other pollutant guidelines were pretty easy for me to stick to. I’m not sure I was presented with Marlin, swordfish or shark during either pregnancy, and I’m not sure I’ve ever managed to get through four cans of tuna in one week! I did reduce my consumption of canned tuna, unless it really was the only thing I fancied. I didn’t eat any raw shellfish, but did continue to eat cooked prawns. And I’m not sure whether I had sushi or not, but given the opportunity would have had some from a reputable source (I love sushi!!).
One last thing:
The guidelines surrounding pollutants in oily fish also apply while breastfeeding.