Food Safety During Pregnancy: The Risks Behind the Rules

This article provides science background only. It is not medical advice and does not substitute for guidance from your healthcare provider.

Pregnancy brings a lot of food rules. Avoid this, heat that to steaming, don’t eat soft cheese. The rules can seem arbitrary without understanding why they exist.

They’re not arbitrary. Pregnancy causes specific, documented changes to immune function. Those changes make certain pathogens more dangerous — not because pregnancy is a fragile state, but because immune suppression that protects the developing fetus also reduces the body’s ability to fight specific infections.

Why Pregnancy Changes Food Safety Risk

Normal immune function treats foreign tissue as a threat and attacks it. A developing fetus is genetically half-foreign — it carries the father’s antigens. Without some immune suppression, the maternal immune system would attack the fetus.

During pregnancy, the immune system downregulates specific cell-mediated immune pathways, particularly T-cell activity in the uterine environment. This protects the fetus. But T-cell immunity is also the primary defense against certain intracellular pathogens — bacteria and parasites that live inside cells, where antibodies can’t reach them.

Listeria monocytogenes, Toxoplasma gondii, and some viral pathogens are intracellular pathogens. They’re disproportionately dangerous during pregnancy for exactly this reason. The immune pathways that normally contain them are partially suppressed.

Listeria: The Primary Concern

The CDC reports that pregnant women are 10 times more likely than the general population to get listeriosis. During pregnancy, that rate rises to 17 times higher per some analyses.

Listeria monocytogenes has two features that make it uniquely dangerous during pregnancy. First, it grows at refrigerator temperatures (as low as 32°F), unlike most foodborne pathogens that require warmer temperatures. Second, it can cross the placental barrier and infect the fetus directly.

Listeria infection during pregnancy can cause:

• Miscarriage or stillbirth
• Preterm labor
• Severe illness or death in the newborn

The infection in the mother may present as mild flu-like symptoms — fever, muscle aches, fatigue. Because the maternal symptoms are often mild, the connection to severe fetal outcomes can be missed.

High-risk foods for Listeria include:

• Ready-to-eat deli meats and hot dogs (unless heated to steaming)
• Soft cheeses made from unpasteurized milk (brie, camembert, queso fresco, feta)
• Unpasteurized dairy products
• Smoked seafood from the refrigerator case
• Raw sprouts
• Pre-made deli salads (potato salad, coleslaw, tuna salad from the deli counter)

The Listeria science article covers the biology of L. monocytogenes in full. The critical difference from other pathogens: refrigeration doesn’t stop Listeria, it just slows it. Ready-to-eat foods that are stored in the refrigerator for extended periods can develop significant Listeria loads even when properly refrigerated.

Salmonella and Eggs

Salmonella infection during pregnancy is not significantly more common than in the general population, but complications can be more severe. Salmonella bacteremia (Salmonella entering the bloodstream) can potentially affect fetal outcomes.

Raw or undercooked eggs and raw or undercooked poultry carry Salmonella risk. The practical guidance healthcare providers typically recommend: cook eggs until both yolk and white are firm, cook poultry to 165°F, and avoid foods made with raw eggs (traditional Caesar dressing, certain aiolis, homemade ice cream with raw egg).

Pasteurized eggs are available at most grocery stores and eliminate the Salmonella risk from eggs used in applications where the egg won’t be cooked.

Toxoplasma

Toxoplasma gondii is a parasite that causes toxoplasmosis. Most healthy adults experience no symptoms. During a primary infection in pregnancy, the parasite can cross the placental barrier and cause severe harm to the developing fetus.

Food sources of Toxoplasma include:

• Raw or undercooked meat, particularly lamb and pork
• Unwashed produce that may have been contaminated with cat feces (Toxoplasma is shed in cat feces by infected cats)
• Unpasteurized goat milk (less common source)

Cooking meat to USDA minimum internal temperatures destroys Toxoplasma. Washing produce thoroughly under running water reduces surface contamination. Freezing meat for several days before cooking also reduces Toxoplasma viability.

Mercury in Fish

Mercury doesn’t involve a pathogen — it’s a heavy metal toxin that accumulates in large, long-lived predatory fish through a process called biomagnification. Larger fish eat smaller fish, concentrating the mercury that was in their prey. Methyl mercury, the organic form found in fish, crosses the placental barrier and concentrates in fetal neural tissue.

Developing brains are more vulnerable to mercury toxicity than adult brains. High mercury exposure during fetal development is associated with neurological developmental problems.

The FDA and EPA have developed specific guidance for fish consumption during pregnancy. The guidance divides fish into three categories:

Best choices (2-3 servings per week): Salmon, shrimp, pollock, tilapia, catfish, canned light tuna, cod, herring, sardines, trout

Good choices (1 serving per week): Canned albacore (white) tuna, halibut, mahi mahi, snapper, grouper

Avoid: Shark, swordfish, king mackerel, tilefish from the Gulf of Mexico, orange roughy, marlin, bigeye tuna

The FDA and EPA’s updated 2024 fish advice emphasizes that avoiding all fish during pregnancy to avoid mercury is unnecessary and counterproductive — fish provides omega-3 fatty acids (particularly DHA), protein, and other nutrients important for fetal development. The guidance is to choose lower-mercury fish and eat the recommended amounts, not to avoid fish entirely.

Practical Guidance

The foods healthcare providers most commonly advise avoiding during pregnancy, based on the risk profile above:

The rules around food during pregnancy exist because specific, documented changes in immune function make specific pathogens more dangerous. Understanding the biology doesn’t change the practical guidance, but it makes following that guidance feel like a reasoned decision rather than an arbitrary restriction.

The information in this article reflects current scientific understanding and regulatory guidance from the CDC, FDA, and ACOG. It does not constitute medical advice. Always discuss your specific dietary choices and concerns during pregnancy with your healthcare provider.