We’re taught that seafood can be an important part of a balanced and healthy diet.

High in Omega-3 fatty acids which aid brain development, fish is a great source of high quality protein.

Here’s where it gets downright confusing. How do you know which fish are safe during pregnancy? And why exactly does it matter? Much of it boils down to methylmercury, a metal that is formed in aquatic systems and gets concentrated as you go up the food chain from bacteria to plankton to fish.

Methylmercury is a concern because it can build up in our bodies over time and pass from your blood into that of your unborn child.

Several studies link high methylmercury levels during pregnancy with subtle developmental deficits in children such as loss of IQ points, attention deficits, and decreased performance on tests of language skills and memory function.

(Paying attention to mercury levels is also important for breastfeeding moms and young children.)

Also, since it takes a while for it to get eliminated from our bodies, it’s important to take precautions with fish consumption even before you get pregnant. It can take up to a year for high methylmercury levels to reach a normal range in humans.

Here’s the Bottom Line:

In general, fish-eating fish such as marlin, swordfish, shark and larger species of tuna (such as yellowfin or ahi), and largemouth bass have higher levels of mercury than herbivorous or smaller fish such as tilapia and herring. ?These large fish should be avoided completely.

It’s considered ok to eat 12 ounces (about 2 average meals) per week of cooked low mercury fish and shellfish. My 5 favorite low mercury choices are shrimp, salmon, catfish, pollock, and canned light tuna. Albacore or “white tuna” has more methylmercury than canned light tuna so if you opt for that, try not to exceed 6 oz per week.

Read more at the FDA on fish safety for pregnant and breastfeeding women as well as young children.