Safe seafood in pregnancy: the mercury guide

Seafood often gets lumped in with the “avoid” list, but that’s only half the story. Fish is genuinely good for you and your baby in pregnancy — it’s a great source of protein and iodine, and oily fish are rich in omega-3 fatty acids (DHA), which are important for your baby’s brain and eye development. So the goal isn’t to avoid seafood, but to choose the right kinds and cook them properly.

There are really two separate things to think about: mercury and food safety.

Mercury. Some fish contain higher levels of mercury, which can affect a developing baby’s nervous system if you eat too much. The amount depends on the type of fish — larger, longer-living predator fish accumulate the most. In Australia, the fish to limit most strictly are shark (flake), swordfish, marlin and broadbill (have these only rarely, if at all). Orange roughy (sea perch) and catfish should be limited too. The good news is that most fish Australians eat regularly are low in mercury and can be enjoyed a few times a week — including salmon, tinned tuna (choose “light” or skipjack, and enjoy in moderation), sardines, prawns, and most common table fish. FSANZ publishes clear, current advice on how many serves of each type are recommended, so it’s the place to check the specifics, as the guidance is detailed.

As a general rule of thumb, aim for two to three serves of low-mercury fish and seafood per week to get the benefits without the mercury risk. Variety helps.

Food safety. Separately from mercury, seafood needs to be handled and cooked safely, because raw and chilled ready-to-eat seafood can carry listeria. So in pregnancy:

• Avoid raw seafood — sushi, sashimi, raw oysters and other raw shellfish.
• Avoid chilled, smoked or pre-cooked ready-to-eat seafood — like smoked salmon, cold cooked prawns from the deli, or seafood in a chilled salad — unless it’s cooked until steaming hot.
• Do eat seafood you cook thoroughly yourself, and freshly cooked hot seafood (like hot chips-shop fish or freshly cooked prawns eaten straight away).
• Tinned fish (tuna, salmon, sardines) is convenient and safe, and a great everyday option — just mind the mercury advice for tuna.

So a typical safe approach looks like: enjoy a couple of serves a week of well-cooked salmon, other low-mercury fish, cooked prawns and tinned fish; skip the sushi, raw oysters and smoked salmon for now; and save shark/flake, swordfish and marlin for after the baby’s born.

It’s worth knowing why the fish is so encouraged, not just tolerated. The long-chain omega-3 fats (especially DHA) in oily fish are building blocks for your baby’s brain, eyes and nervous system, particularly in the later months when their brain develops fastest — and getting enough is linked with benefits for your baby. That’s why the advice is to keep eating fish (the right kinds, well cooked) rather than cutting it out; the benefits of including it outweigh the small, manageable mercury risk when you choose low-mercury types.

A couple of popular items cause confusion, so to be clear: cooked sushi (like fully cooked teriyaki chicken or cooked-prawn rolls, or fresh vegetable and avocado rolls) can be fine, but raw-fish sushi and sashimi are best avoided, as is cold smoked salmon unless it’s cooked hot. Freshly cooked prawns eaten hot are great; cold cooked prawns from a deli or a platter that’s been sitting out are the ones to skip. When you’re unsure at a restaurant, ask for it freshly cooked and served hot, and you’re on safe ground.

If you don’t eat much fish — because you don’t like it, or you’re vegetarian or vegan — you can still get omega-3s from sources like chia seeds, walnuts, flaxseed and algae-based supplements, and it’s worth chatting to your GP, midwife or a dietitian about whether a supplement would help. Either way, seafood is a food to enjoy thoughtfully in pregnancy, not to fear — the key is choosing low-mercury types and cooking them well.