Are fish containing mercury unsafe for pregnant women?

From the Guidelines

Pregnant women should limit or avoid fish high in mercury, as it can harm the developing fetus, and instead opt for low-mercury fish such as salmon, shrimp, pollock, tilapia, catfish, cod, and canned light tuna, aiming for 8-12 ounces (2-3 servings) weekly. High-mercury fish to avoid include shark, swordfish, king mackerel, tilefish, bigeye tuna, marlin, and orange roughy [ 1 ]. Mercury is particularly concerning during pregnancy because it can cross the placenta and affect fetal brain development, potentially causing developmental delays and neurological problems [ 1 ]. Local fish advisories should also be checked, as mercury levels can vary by location [ 1 ]. Proper cooking doesn't eliminate mercury, as it binds to the protein in fish tissue, so choosing low-mercury species is essential. The benefits of fish consumption, including omega-3 fatty acids and nutrients, outweigh the risks when low-mercury fish are consumed in moderation, as supported by the most recent evidence [ 1 ].

Key Considerations

• Mercury levels in fish can vary by location and species
• Pregnant women should check local fish advisories for guidance on safe fish consumption
• Low-mercury fish options are available and can provide essential nutrients and omega-3 fatty acids
• High-mercury fish should be avoided due to potential harm to the developing fetus

Recommendations

• Pregnant women should aim for 8-12 ounces (2-3 servings) of low-mercury fish weekly
• Limit or avoid high-mercury fish, including shark, swordfish, king mackerel, tilefish, bigeye tuna, marlin, and orange roughy
• Choose low-mercury fish options, such as salmon, shrimp, pollock, tilapia, catfish, cod, and canned light tuna
• Check local fish advisories for guidance on safe fish consumption [ 1 ]

From the Research

Mercury in Fish and Pregnancy

• Fish containing high levels of mercury are considered unsafe for pregnant women, as mercury can have detrimental effects on the developing fetus 2, 3.
• The FDA recommends that pregnant women avoid eating shark, swordfish, mackerel, and tilefish, which often harbor high levels of methylmercury, a potent human neurotoxin 2.
• However, fish with low levels of mercury and high levels of omega-3 fatty acids, such as EPA and DHA, are considered beneficial for pregnant women and can provide essential nutrients for fetal development 4, 5.

Benefits of Fish Consumption During Pregnancy

• Maternal ingestion of adequate quantities of fish has been associated with better childhood IQ scores, fine motor coordination, and communication and social skills, along with other benefits 4.
• Fish consumption during pregnancy may have a protective effect on birthweight, and moderate mercury levels in pregnancy were not associated with anthropometric variables or the odds of low birthweight or preterm birth 6.
• Women of childbearing age can consume certain fish species every day or often and remain below toxicological benchmarks for mercury, while also attaining the recommended DHA level 5.

Guidelines for Fish Consumption During Pregnancy

• Pregnant women should be advised to eat fish to benefit from naturally occurring omega-3 fatty acids, to avoid fish with high levels of mercury and other contaminants, and to choose fish with high levels of EPA and DHA 4.
• Government advice on fish consumption during pregnancy includes information on fish species to avoid and to limit, while encouraging consumption of at least two portions of fish per week 6.