Raw fish poses three distinct threats during pregnancy: bacterial infections that can cross the placenta, parasites that cause severe gastrointestinal illness, and mercury that accumulates in fetal brain tissue. The risks are dramatically higher than for non-pregnant adults because pregnancy fundamentally changes how your immune system works, leaving you more vulnerable to pathogens that a healthy body would normally fight off.
Pregnancy Changes Your Immune System
During pregnancy, hormonal shifts suppress part of your immune response, specifically the cell-mediated branch that targets bacteria and parasites inside your own cells. This suppression isn’t a flaw. It’s what prevents your body from rejecting the fetus, which carries foreign DNA. But it comes with a tradeoff: infections that would cause mild symptoms in a non-pregnant person can become serious or even life-threatening during pregnancy.
This immune shift makes pregnant women especially vulnerable to two foodborne pathogens commonly found in raw seafood: Listeria monocytogenes and Salmonella enterica. Both can trigger complications ranging from severe dehydration to preterm labor, and in the case of Listeria, direct infection of the fetus.
Listeria Is the Most Dangerous Threat
Listeria is the primary reason raw fish is off the table during pregnancy. Unlike most bacteria, Listeria thrives at refrigerator temperatures, so cold storage doesn’t protect you. It also has an unusual ability to cross the placental barrier and directly infect the fetus or the amniotic fluid.
The consequences of fetal Listeria infection are severe. In a 10-year hospital study published in the Journal of Inflammation Research, the overall fatality rate among offspring of mothers with perinatal listeriosis reached 71.88%. Nearly half of all fetuses (46.88%) died before or during birth, and among the babies born alive, another 47% did not survive. Infections in the second trimester were particularly devastating, with a 92% fatality rate among offspring. Third-trimester infections carried a fatality rate of about 53%.
Among mothers in that study, 57% delivered prematurely and 25% miscarried before 28 weeks. Even babies who survived often had Listeria in their bloodstream: 65% of live births tested positive, and over 40% had confirmed bacterial infection in their blood.
Listeriosis has an unusually unpredictable incubation period, ranging from 24 hours to 70 days after exposure. That long window means you may not connect your symptoms to something you ate weeks earlier. Treatment typically requires several weeks of antibiotics, and some experts recommend continuing treatment for three to four weeks because the bacteria can hide inside cells and within the placenta, potentially rebounding after a shorter course.
Parasites in Raw Fish
Raw and undercooked fish can harbor parasitic worms, most notably Anisakis simplex. When swallowed alive, these larvae burrow into the stomach or intestinal lining, causing intense abdominal pain, nausea, vomiting, and in some cases allergic reactions. For a pregnant woman already dealing with immune suppression, this kind of acute gastrointestinal crisis raises the risk of dehydration and complications.
Research on Anisakis antibodies in pregnant women has confirmed that the mother’s immune response to the parasite transfers across the placenta to the fetus. While the long-term effects of this fetal sensitization aren’t fully understood, fish intake during pregnancy has been linked to concerns including fetal growth restriction and potential allergic sensitization.
Commercial freezing does kill parasites effectively. The FDA requires fish intended for raw consumption to be frozen at -4°F (-20°C) for seven days, or blast-frozen at -31°F (-35°C) until solid and stored for at least 15 to 24 hours depending on holding temperature. Sushi-grade fish at reputable restaurants has typically undergone this treatment. However, freezing does nothing to kill bacteria like Listeria, which is why even previously frozen raw fish still carries risk during pregnancy.
Mercury Builds Up in the Fetal Brain
Mercury in fish exists primarily as methylmercury, a form that your intestines absorb almost completely. Once in your bloodstream, it crosses both the placenta and the fetal blood-brain barrier. The fetus actually accumulates more mercury than the mother: cord blood concentrations are higher than maternal blood levels, and the developing brain clears mercury less efficiently than an adult brain does.
This matters because the first years of life represent a critical window of brain development. Harmful concentrations can build up during this vulnerable period, potentially affecting neurological development. The concern isn’t limited to raw fish (cooked high-mercury fish poses the same risk), but many of the species popular in sushi and sashimi, like bigeye tuna, are among the highest-mercury options.
Fish to Avoid Entirely
The FDA lists seven types of fish with the highest mercury levels that pregnant women should not eat in any form, raw or cooked: king mackerel, marlin, orange roughy, shark, swordfish, tilefish from the Gulf of Mexico, and bigeye tuna.
Lower-Mercury Options
Salmon, shrimp, cod, tilapia, catfish, sardines, anchovies, pollock, and canned light tuna (skipjack) all fall into the FDA’s “best choice” category for lowest mercury. These are safe to eat two to three servings per week when fully cooked. Fish like yellowfin tuna, halibut, snapper, mahi mahi, and grouper have moderate mercury and are considered a “good choice” at one serving per week.
Sushi Restaurants Add Cross-Contamination Risk
Even if you order a cooked roll or a vegetarian option at a sushi restaurant, cross-contamination is a real concern. Sushi preparation involves extensive handling of both raw and cooked ingredients on the same surfaces, with the same tools, and often by the same hands. Cutting boards, knives, bamboo rolling mats, and prep surfaces can transfer bacteria from raw fish to otherwise safe ingredients. Health guidelines recommend that bamboo mats be lined with food-grade plastic wrap and changed every two hours or after any contact with raw fish, but enforcement varies by establishment.
Safe Alternatives You Can Still Enjoy
You don’t have to give up sushi restaurants entirely. Cooked sushi options are widely available and can satisfy the craving without the risk. Shrimp tempura rolls use fully cooked shrimp. Unagi (freshwater eel) is always grilled before serving. Cooked crab is a common filling in California rolls, though you should confirm the restaurant uses real crab rather than preparing it alongside raw fish on the same board.
Fully cooked shellfish, including shrimp, crab, lobster, scallops, mussels, clams, and oysters, are all low in mercury and safe during pregnancy as long as they’re heated through. Vegetable rolls with avocado, cucumber, or sweet potato are another option, though it’s worth asking how they’re prepared relative to the raw fish station.
If you’re eating at home, cooking fish to an internal temperature of 145°F kills both bacteria and parasites. Salmon, cod, and shrimp are quick to prepare, low in mercury, and high in the omega-3 fatty acids that support fetal brain development. The goal isn’t to avoid fish altogether. It’s to eat it cooked, from lower-mercury species, two to three times a week.