Is king mackerel safe during pregnancy?

What does the evidence say about king mackerel during pregnancy?

1. King mackerel is named on the 'Choices to Avoid' list for pregnancy and breastfeeding, grouped with bigeye tuna, shark, swordfish, marlin, Gulf of Mexico tilefish, and orange roughy as the fish with the highest mercury levels. 1
2. A review of national fish-in-pregnancy guidance places king mackerel in the 'do not eat' category for US recommendations, while Spanish mackerel falls into a 'limit' category and Atlantic mackerel is grouped with the 'eat freely' best-choices fish, showing the mercury risk depends on which mackerel is on the plate. 2
3. Very high methylmercury exposure from diet has been shown to increase the chance of a baby having a smaller head size, brain damage, developmental delay, or intellectual disability, which is the basis for keeping the highest-mercury fish off the plate during pregnancy. 1
4. When fish is kept to low-mercury choices, moderate intake of about one to three servings a week during pregnancy was linked to beneficial neurodevelopmental outcomes for the child in most of the observational studies a systematic review examined. 3
5. A pregnant woman who follows FDA advice on eating fish, choosing amounts and species within the recommended guidance, is not likely to have a child with learning or behavior problems from methylmercury exposure. 4

Is king mackerel safe in each trimester?

• First trimester. Avoiding king mackerel from the start makes sense because methylmercury crosses the placenta throughout pregnancy and the body clears it slowly, so exposure earlier on still matters later.
• Second trimester. If king mackerel has already been part of your routine, switching to a Best Choices fish like salmon, sardines, or Atlantic mackerel from here forward still lowers your overall mercury exposure for the rest of pregnancy.
• Third trimester. Fetal brain growth continues rapidly in the third trimester, which is exactly why king mackerel stays on the avoid list through delivery rather than the guidance easing up as pregnancy progresses.