Risk of Listeria Infection

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Listeria is a type of bacteria that can contaminate food, causing food poisoning (also called listeriosis). 

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Listeria infection can have serious health impacts for pregnant women and the growing fetus, and can be more serious than for the non-pregnant population. It is estimated that pregnant women are at 20x greater risk of listeria infection than the general population. Doctors usually test if a pregnant woman has a listeria infection through a blood test.
 
Pregnant women who contract listeriosis usually develop a mild flu-like illness, with fever and headache. However, a listeria infection in the pregnant woman can be transferred through the placenta to the developing fetus and the impacts of listeria infection are more severe for the developing fetus, with an overall fetal fatality of 20-30%. The fetus’ immune system may not be fully developed enough to fight off the listeria bacteria. 

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In addition to fetal loss, listeriosis in pregnant women is also associated increased risk of illness in the newborn, such as meningitis and sepsis in newborns. Of infants born to pregnant mothers infected with listeria, just over 60% completely recovered. If listeriosis is detected in the pregnant women and treated with antibiotics, the impacts of fetal health can be prevented.

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High cooking temperatures kill the listeria bacteria in food. Food that is ready-to-eat without further cooking or food that is unprocessed are at risk of listeria contamination.

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Pregnant women should avoid:

 

• Unpasteurized foods: unpasteurized dairy products, cheeses and fruit juices / ciders

• Pre-packed foods: fruit or vegetables salads, deli meats, prepared meals

• Raw or uncooked foods: raw sprouts, meats, poultry, seafood (e.g. sushi), shellfish and eggs

• Refrigerated foods that do not require further cooking: pâtés, meat spreads and smoked seafood

• Soft cheeses: feta, brie, camembert, blue-veined, Mexican-style cheeses

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Health Canada recommends that, in addition to avoiding these food products, pregnant women should minimize their risk of food poisoning through careful cleaning of foods, kitchen equipment and reusable grocery bags, separate foods, cook food to a safe internal temperature and promptly chill food and leftovers to an adequate temperature. 

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High Mercury Levels

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Omega-3 (alpha-linolenic acid) and omega-6 (linoleic acid) fatty acids are referred to as essential fatty acids, meaning that they must be consumed in your diet. Our bodies do not make these fatty acids on their own. The body requires a proper balance of omega-3 and omega-6 levels to support a variety of functions, including complex cell signaling.

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Pregnant women are recommended to consume proper amounts of fatty acids in their diets, as omega-3 is critical to support the fetal brain and eye development.

 

Health Canada encourages pregnant women to consume fish during pregnancy (at least 150 grams of cooked fish per week), as fish are an excellent source of omega-3 fatty acids. Fish are also high in protein, as well as vitamins and minerals, including Vitamin D.

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However, it is important to choose fish that are low in mercury and other contaminants. Mercury can build up in fish through exposure to their environment and from the prey they eat – therefore, fish that are larger in size and are predatory have increased mercury levels. When pregnant women consume these types of fish, the organic form of mercury, known as methyl mercury, can cross the placenta and enter the fetus’ blood stream. Methyl mercury can have damaging effects on the fetus’ central nervous system. Scientists have shown that high mercury levels in the pregnant woman’s blood is associated with long-term impacts on the child’s health, including cognitive development.

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Health Canada recommends that pregnant women:
 

• Limit the consumption of predatory fish that contain higher levels of methyl mercury to no more than 150 grams per month, including fresh and frozen tuna, shark, swordfish, marlin, orange roughy and escolar

• Limit intake of canned (white) albacore tuna to no more than 300 grams per week

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High Vitamin A Levels

 

Health Canada recommends a healthy diet during pregnancy that includes fruits and vegetables with high levels of beneficial vitamins and minerals to support fetal growth and development. Vitamin A is critical to support fetal development, including development of the eyes, bones, teeth, hair and immune system. Vitamin A is found in dark green and orange vegetables and fruits.

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As pregnancy progresses, there is an increasing demand for Vitamin A. However, high levels of Vitamin A are associated with birth defects, especially if consumed early in pregnancy. These defects most commonly involve the fetus’ nervous system and cardiovascular system, and is associated with miscarriage.

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It is therefore recommended that Canadian pregnant women:
 

• Avoid Vitamin A or fish liver oil supplements

• Limit food products high in Vitamin A levels, including liver and liver products

• Avoid prenatal supplements that contain more than 10,000 international units of preformed Vitamin A (including acetate, succinate, palmitate)

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