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The "Eat Fish", "Don't Eat Fish" Dilemma of Pregnancy

When you’re pregnant, it’s hard to escape the eat fish, don’t eat fish dilemma.

On the one hand, pregnant women are told that fish–rich in iodine, selenium, and omega-3 fatty acids, and other vital nutrients–is good for our babies’ rapidly growing brains.

Recent studies have linked fish consumption during pregnancy with faster processing times and better memory, less hyperactivity and impulsiveness, as well as higher overall cognitive scores on standard tests of development.

But we are also told that fish, which can contain high levels of mercury, is potentially toxic for our babies’ rapidly growing brains. Children exposed to high mercury levels during pregnancy may suffer from lower IQ scores and reduced ability to focus.

So, what’s a smart mama-to-be to do?

Do keep eating fish.

The FDA and EPA recommend that pregnant women eat two to three 4 oz. servings (8-12 oz.) of fish each week.

The key is to eat the right kind of fish.

The benefits of eating fish during pregnancy outweigh the harms, provided you eat fish low in mercury. In a study recently published in JAMA Pediatrics, consuming fish at least twice a week during pregnancy lowered children’s risk of ADHD. At the same time, higher levels of mercury in women during pregnancy raised their children’s risk of ADHD.

Another recent study found that although eating fish during pregnancy was linked with higher IQ scores at age 3, higher levels of mercury during pregnancy correlated with lower IQ scores at age 3.

In light of these apparent benefits of eating fish during pregnancy for children’s later cognitive development, many public health officials worry that pregnant women in the U.S. are eating too little fish, not too much.

Avoid high mercury fish before, during, and after pregnancy.

Public health messages understandably focus on pregnancy, a time of rapid development, but the advice is similar for those who are not pregnant.

Women who are planning to become pregnant or who are breastfeeding should also avoid high mercury fish. So should young children.

There are seven fish in the FDA’s Avoid category.

THE Avoid category—High Mercury fish:

  • Tuna (bigeye)
  • Swordfish
  • King mackerel
  • Shark
  • Orange roughy
  • Marlin
  • Tilefish (from the Gulf of Mexico).

Don’t panic if you accidentally consumed some Avoid fish. The harms of mercury don’t occur with a single serving of swordfish. One oops is nothing to fret over. Instead,  just get back on the low mercury bandwagon and keep trucking.

Don’t assume you can supplement and forget it.

Can’t you just bypass this problem by taking an omega-3 fatty acid supplement?

Sadly, probably not. Randomized trials do not show that omega-3 fatty supplements provides the same benefits as those linked with actually eating fish.

mercury fish pregnancy

Choosing the Right Fish

The FDA classifies all fish according to potential mercury levels.

Outside of the Avoid category, all other fish fall into either the Best or Good categories. 

Here’s where you have some wiggle room. For me personally while pregnant, I stuck with the Best category and skipped fish the FDA considered merely “Good “for a couple of reasons:

  1. By eating only the Best fish, you can eat more fish, and that’s a good thing. In most studies, the benefits of eating fish during pregnancy and breastfeeding kick in at higher levels of fish consumption, usually two or more 4 oz. servings of fish a week. The FDA only recommends eating fish labelled Best that often. If you choose fish labelled Good category, you’re supposed stick with just one serving a week–likely not enough to gain those health benefits.
  2. You’re playing it safe. The fish categories aren’t based on the testing of that many samples of each kind of fish. So it’s always possible some fish will exceed the tested levels. By eating very low mercury fish, you lower the chances of accidentally getting more mercury than expected.

The BEST category—Low mercury fish:

  • Salmon
  • Cod
  • Whitefish
  • Anchovies
  • Canned light tuna
  • Shrimp
  • Crab
  • + 30 more (Click here to see the full chart.)

Another rule of thumb: Steer clear of fish caught in local waters. Many local lakes and rivers are contaminated with mercury and other harmful pollutants like PCBs. If you don’t know where your fish was caught, take a pass. Generally speaking, it’s safest to stick with ocean fish.

If you do eat fish caught in waters without local guidance, it’s best to limit your consumption of those fish, and avoid all other fish that week. (The FDA provides age-appropriate servings of these fish here.)

mercury pregnancy

The Hazards of Mercury While Pregnant

Why worry about mercury in fish at all? Is it yet another exaggerated fear created, it seems, just to plague pregnant women?

Sadly, no. Just by eating fish a few times a week, you can exceed mercury levels the EPA deems safe during pregnancy.  An estimated 1 in 12 women of childbearing age have mercury levels that exceed the EPA’s limits. And among women who eat fish 3 or more times a week, nearly 1 in 3 exceed the EPA limits.

These levels may be dangerous for your growing baby’s brain. Mercury is a potent neurotoxin, whose effects are especially profound in the unborn. Mercury not only damages their existing neurons, it can prevent their neurons from growing in the first place.

Extreme cases of exposure to mercury in utero have led to devastating birth defects among Japanese children living in Minamata City in the 1950s and 1960s and among Iraqi children exposed to a mercury-based fungicide in the early 1970s. Lower levels of mercury have been linked with poorer attention span, increases hyperactivity, and higher risk of a below normal IQ. As with lead, there is no clear safe level of mercury exposure. The lower, the better.

The Bigger Picture

It’s easy to see this issue as just another pain in the butt part of pregnancy. No wine, no beer, no skiing, no deli meats, and check the Internet before ordering seafood.

And it’s true. In the grand scheme of things, we are lucky to know about this issue, and even luckier to be able to work around it—advantages which the majority of pregnant women around the world notably lack.

And that’s why this problem is worth complaining about. We shouldn’t have to perform a delicate dance to avoid a potent neurotoxin in the first place. Mercury is a naturally occurring element, but the methyl mercury found in fish does not derive from natural sources. It comes from pollution. In the U.S., mainly from coal and oil-fueled power plants which lack modern pollution controls.

Mothers and babies everywhere deserve so much better.

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About Amy

Amy Kiefer is a researcher by training, and earned her Ph.D. from the University of Michigan. She currently lives in the Bay Area with her husband and three children where she writes about fertility, pregnancy, and breastfeeding. Check out her blog, expectingscience.com, for more great evidence-based pregnancy and parenting info.

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