Tuna is considered a great source of nutrients, many of which are especially important during pregnancy. 

For instance, it’s commonly praised for its eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) content — two long-chain omega-3 fats that play crucial roles in the development of your baby’s brain and nervous system (1).

Nonetheless, most types of tuna also contain high levels of mercury, a compound linked to various health and developmental problems in babies. For this reason, women are often warned to limit the amount of tuna they eat during pregnancy. 

This article reviews whether it’s safe to eat tuna while pregnant, and if so, in what amounts. 

Tuna contains nutrients important for a healthy pregnancy

Tuna is rich in a variety of nutrients, many of which are important throughout your pregnancy. Those present in the largest amounts include (2):

  • Protein. This nutrient is important for all aspects of growth. Eating too little protein during pregnancy may result in miscarriage, intrauterine growth restrictions, and low birth weight. That said, excess protein may have similar negative effects (3).
  • EPA and DHA. These long-chain omega-3s are crucial for a baby’s eye and brain development. Long-chain omega-3s may also reduce the risk of preterm birth, poor fetal growth, maternal depression, and childhood allergies (1, 4, 5, 6).
  • Vitamin D. Tuna contains small amounts of vitamin D, which is important for immunity and bone health. Adequate levels may also lower the risk of miscarriage and preeclampsia — a complication marked by high blood pressure in pregnancy (7, 8, 9, 10).
  • Iron. This mineral is important for the healthy development of your baby’s brain and nervous system. Adequate levels during pregnancy may also reduce the risk of low birth weight, preterm birth, and maternal mortality (11, 12).
  • Vitamin B12. This nutrient helps optimize nervous system function and make protein and oxygen-transporting red blood cells. Low levels during pregnancy may raise the risk of miscarriage, preterm birth, birth defects, and other pregnancy complications (12, 13, 14).

One 3.5-ounce (100-gram) portion of light canned tuna provides around 32% of the Reference Daily Intake (RDI) for protein, 9% of the Daily Value (DV) for iron, and 107% of the DV for vitamin B12 (2, 12, 15, 16).

This portion also contains around 25 mg of EPA and 197 mg of DHA, which amounts to around 63–100% of the daily amount most experts recommend that pregnant women consume (2, 17, 18).

Pregnant women who do not eat tuna due to food allergies, as well as religious or ethical reasons, should ensure they get enough of these nutrients from other sources. 

They may also benefit from taking a daily supplement providing at least 200 mg of DHA or 250 mg EPA plus DHA per day (18).

summary

Tuna is a convenient source of protein, long-chain omega-3s, vitamin D, iron, and vitamin B12. Getting enough of these nutrients during pregnancy may reduce your risk of pregnancy complications and improve birth outcomes. 

Why tuna may be dangerous during pregnancy

Most health professionals recommend that women who normally eat tuna continue to do so during pregnancy. That said, due to its mercury content, they warn pregnant women to avoid eating too much of it. 

Although it’s a natural compound, most of the mercury found in fish is the result of industrial pollution, and its levels in fish appear to rise each year (19).

All fish contain some mercury, but the larger, older, and higher up on the food chain a fish is, the more mercury it’s likely to contain. Tuna is a predatory fish that can grow big and old. Hence, most types accumulate significant amounts of mercury in their flesh (20).

High intakes of mercury during pregnancy can harm the development of your baby’s brain and nervous system. This can result in a range of problems, the most common of which include (21, 22, 23): 

  • learning difficulties
  • delayed motor skill development
  • speech, memory, and attention deficits
  • poor visual-spatial abilities
  • lower intelligence quotients (IQs)
  • high blood pressure or heart problems in adulthood

In severe cases, high intakes of mercury during pregnancy sometimes result in loss of smell, vision, or hearing in the infant, as well as birth defects, seizures, coma, and even infant death (21).

Interestingly, some research suggests that mercury exposure in early pregnancy may have no negative effects on a child’s behavior, development, or brain function, as long as the mother ate fish during pregnancy (24).

This suggests that certain compounds in fish may counterbalance the negative effects of mercury. However, more research is needed before strong conclusions can be made.

Moreover, pregnant women should avoid eating raw tuna to minimize their risk of infection with Listeria monocytogenes, a bacteria that can have devastating effects on an infant’s growth and development (25).

summary

Tuna is a fish that often contains high levels of mercury. Ingesting too much mercury during pregnancy can harm the development of your baby’s brain and nervous system, ultimately resulting in a range of health and developmental problems. 

How much tuna is considered safe during pregnancy?

Mercury risk is cumulative, and different types of fish contain different amounts of mercury.

As such, the Food and Drug Administration (FDA) suggests that pregnant women consume 8–12 ounces (225–340 grams) of fish and seafood per week, including no more than either of the following (26):

  • 12 ounces (340 grams) of canned light tuna or other low mercury fish, such as anchovies, cod, tilapia, or trout

or

  • 4 ounces (112 grams) of yellowfin, white, albacore tuna, or other medium mercury fish, such as bluefish, halibut, mahi-mahi, tilefish, or snapper

Moreover, pregnant women are encouraged to completely avoid bigeye tuna and other high mercury fish, such as swordfish, shark, marlin, orange roughy, king mackerel, and tilefish. 

Many international food authorities have also issued recommendations regarding tuna consumption during pregnancy. Many are very similar to the FDA guidelines, though the type of tuna considered safe for consumption varies between countries (27).

summary

The amount of tuna considered safe during pregnancy varies by country. In the United States, women are advised to eat no more than 12 ounces (340 grams) of canned light tuna or less than 4 ounces (112 grams) of yellowfin or albacore tuna per week. 

The bottom line

Tuna is a convenient source of nutrients, many of which are especially important during pregnancy. 

However, certain varieties of tuna can contain high levels of mercury, a compound that may harm your baby’s health and result in a range of developmental problems. Moreover, eating raw tuna can increase the risk of a Listeria infection.

To maximize the benefits of eating tuna while minimizing any risks, pregnant women are encouraged to avoid eating raw tuna. They should also favor low mercury types of tuna and other fish while avoiding ones with high mercury levels.

Women who bypass eating tuna due to allergies or religious or ethical reasons would likely benefit from adding a long-chain omega-3 supplement to their diet.