Learn about foodborne illness and how to prevent certain foodborne risks during your pregnancy.
Methylmercury: Frequently Asked Questions
"What is methylmercury?"
It's a metal that can be found in certain fish. The methylmercury in these fish can be harmful to your unborn baby if you eat these fish. Mercury occurs naturally in the environment and can also be released into the air through industrial pollution. It falls from the air and can get into surface water, accumulating in streams and oceans. Bacteria in the water cause chemical changes that transform mercury into methylmercury, which can be toxic. Fish absorb methylmercury as they feed on aquatic organisms.
"Is there methylmercury in all fish?"
Nearly all fish contain traces of methylmercury. However, larger fish that have lived longer have the highest levels of methylmercury because they've had more time to accumulate it. These large fish pose the greatest risk to pregnant women who eat them regularly.
"How could I become exposed to methylmercury?"
Fish in the diet is the major source of methylmercury, and eating certain types of fish leads to the accumulation of methylmercury in the body. Methylmercury can build up in your blood stream, and can then pass from your blood into that of your unborn child.
Methylmercury is removed from the body naturally, but it may take over a year for the levels to drop to a safe level. Thus, it may be present in a woman even before she becomes pregnant. This is one of the reasons that women who are trying to become pregnant should also avoid eating certain types of fish.
"How can I tell if I've been exposed to methylmercury?"
You will not show noticeable symptoms from eating commercial seafood, but your newborn may experience symptoms (see next question).
"How could methylmercury affect my baby?"
Some fish and shellfish contain higher levels of methylmercury that may harm an unborn baby or young child's developing nervous system.
"What types of fish should I avoid eating while I'm pregnant or trying to become pregnant?"
You, along with nursing mothers and young children, should not eat the following fish, as they can contain high levels of methylmercury:
- King mackerel
It's okay to eat other cooked fish/seafood as long as you select a variety of other kinds while you're pregnant or trying to become pregnant. You can eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in methylmercury. Five of the most commonly eaten fish and shellfish that are low in methylmercury are shrimp, canned light tuna, salmon, pollock, and catfish. Another commonly eaten fish, albacore ("white") tuna has more methylmercury than canned light tuna. So, when choosing your two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of albacore tuna per week.
Note: If you have questions about methylmercury, ask your doctor or healthcare provider.