Methylmercury In Fish


The information provided below is for readers based in the United States of America. Readers outside of the United States of America should seek the information from local sources.

What is methylmercury in fish?

Mercury is a chemical element that exists as exists as part of various chemical compounds. Methylmercury is a type of organic mercury compound. Resulting mostly from industrial pollution of bodies of water, organic mercury is the most toxic type of mercury and it contaminates fish in particular. Amounts of methylmercury vary between different types of fish, and the risk of mercury contamination must be weighed against established benefits of eating seafood while pregnant. These benefits result from the presence of healthy fats and high quality protein in fish, so the trick is to choose the safest fish and to eat them in optimal amounts.

Is there a safe amount of methylmercury to which I can be exposed during pregnancy?

In the past, pregnant women were advised not to eat fish, due to the danger of methylmercury contamination. More recently, pregnant women have been advised the opposite, that they should consume fish, as it is an excellent source of omega-3 polyunsaturated fatty acids (PUFAs), particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are important in the development of the developing baby’s brain. Currently, the American College of Obstetricians and Gynecologists (ACOG) recommends that pregnant women do consume fish in particular quantities, paying attention to the type of fish.

Fish that usually contain high mercury levels and that should be avoided during pregnancy include swordfish, king mackerel, marlin, orange roughy, shark, and Gulf of Mexico tilefish. Fish that are lower in mercury include salmon, shrimp, tilapia, canned-light, yellow fin tuna, catfish, and cod. ACOG recommends that pregnant women consume 8-12 ounces (225-340 grams, 4-6 portions) of low mercury fish per week. This is more than the amount of fish that pregnant women consume on average. Certain fish, such as albacore tuna are considered to carry medium risk of methylmercury contamination; it is alright for you to consume one portion per week of medium risk fish, but to that you should add a few portions of low mercury fish.

Can exposure to methylmercury make it harder for me to get pregnant?

Studies have shown a correlation between mercury levels in the bloodstream of women with levels of luteinizing hormone (LH), which comes from the pituitary gland and is vital for the function of the ovaries in females and the testes in males. Rodent studies and tests on women undergoing in vitro fertilization suggest that methylmercury may suppress ovarian function and reduce fertility. You and your male partner can reduce the possibility of reduced fertility by avoiding fish with high mercury risk, such as swordfish, king mackerel, marlin, orange roughy, shark, and Gulf of Mexico tilefish, and by opting instead for low-mercury fish, such as salmon and tilapia.

Can methylmercury cause a miscarriage?

Some research suggests that it is possible that consumption of extremely high levels of methylmercury can cause spontaneous abortion (miscarriage), as well as other abnormal pregnancy outcomes such as stillbirth. Such levels are much higher than what you get from eating generous portions of low-mercury fish, such as salmon and tilapia.

Can methylmercury consumption during my pregnancy cause a birth defect?

There is a possibility of birth defects from exposure to high levels of methyl mercury – a study of Chinese pregnancies and babies has revealed a possible association between methylmercury toxicity and neural tube defects (incomplete closure of the bone around the brain or spinal cord).

Are there long-term consequences to my baby from my methylmercury consumption?

Research suggests that methylmercury toxicity from mothers who eat contaminated fish can interfere with the formation of the developing baby’s brain, leading to problems with the childs cognition (ability to think). The benefits of consuming omega-3 fatty acids in the fish balance the risk of the methylmercury, but you can reduce the risk by consuming fish that have low levels of mercury (such as salmon and tilapia), while avoiding high-risk types of fish.

I just found out I am 6 weeks pregnant and last weekend I consumed fish in the high risk category for  methylmercury contamination. Will my baby have a problem?

Overall, eating cooked fish is good for your baby, but if you consumed a high-mercury fish such as tilefish or shark last weekend, from this point you should consume only fish with low mercury levels, such as salmon, tilapia, shrimp, certain types of tuna (canned-light, yellow fin), catfish, and cod, and you should have a few portions per week.

Is it ok to consume some methylmercury after the first trimester?

Throughout pregnancy you should eat only low-mercury fish, a few portions per week.

How will I know if methylmercury has hurt my baby?

In the even that you develop methylmercury toxicity from consuming contaminated fish, any learning and behavioral problems developing in the child might be linked to your consumption of the fish.

Can I consume methylmercury while breastfeeding?

While breastfeeding, you should consume plenty of low-mercury fish, but not high-mercury fish – just like during pregnancy.

What if the father is exposed to methylmercury prior to conception?

There is some possibility that mercury contamination from seafood can affect the male testes in ways that will make conception more difficult to achieve.

Resources for methylmercury in pregnancy:

For more information about methylmercury during pregnancy, contact (800-994-9662 [TDD: 888-220-5446]) or read the following articles:


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General information

It is very common for women to worry about having a miscarriage or giving birth to a child with a birth defect while they are pregnant. Many decisions that women make about their health during pregnancy are made with these concerns in mind.

For many women these concerns are very real. As many as 1 in 5 pregnancies end in a miscarriage, and 1 in 33 babies are born with a birth defect. These rates are considered the background population risk, which means they do not take into consideration anything about the health of the mom, the medications she is taking, or the family history of the mom or the baby’s dad. A number of different things can increase these risks, including taking certain medications during pregnancy.

It is known that most medications, including over-the-counter medications, taken during pregnancy do get passed on to the baby. Fortunately, most medicines are not harmful to the baby and can be safely taken during pregnancy. But there are some that are known to be harmful to a baby’s normal development and growth, especially when they are taken during certain times of the pregnancy. Because of this, it is important to talk with your doctor or midwife about any medications you are taking, ideally before you even try to get pregnant.

If a doctor other than the one caring for your pregnancy recommends that you start a new medicine while you are pregnant, it is important that you let them know you are pregnant.

If you do need to take a new medication while pregnant, it is important to discuss the possible risks the medicine may pose on your pregnancy with your doctor or midwife. They can help you understand the benefits and the risks of taking the medicine.

Ultimately, the decision to start, stop, or change medications during pregnancy is up to you to make, along with input from your doctor or midwife. If you do take medications during pregnancy, be sure to keep track of all the medications you are taking.

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