Listeria monocytogenes is a pathogenic bacterium which causes a group of diseases collectively known as Listeriosis. Listeriosis in pregnancy is characterised by diarrhoea, headache, fever, muscle pain, meningitis, septicaemia, as well as spontaneous abortion.
Listeria monocytogenes can grow at refrigeration temperatures but is killed by cooking and pasteurisation. Therefore, unpasteurised milk and unpasteurised dairy products are not recommended during pregnancy. Some refrigerated foods with a long shelf life (greater than 5 days) which are consumed without further cooking also have a high risk of contamination since L. monocytogenes can grow at refrigeration temperatures.
Toxoplasmosis is caused by the bacterium Toxoplasma gondii and infection is caused by ingestion of Toxoplasma oocytes excreted in cat faeces, or by eating raw or under cooked meat with visible cysts. Infection with this bacterium during pregnancy can result in the transfer of the bacterium to the foetus and result in spontaneous abortion or serious handicap in the newborn.
Raw or undercooked meats, poorly fermented or cured meats, and unwashed fruit and vegetables are potential sources of this bacterium and should be avoided during pregnancy.
Meat should be well cooked (no pink meat) and served piping hot to prevent Toxoplasma gondii infection. Hand washing (especially after handling raw meat and unwashed vegetables) and other hygiene practices are of utmost importance as well as wearing gloves when gardening or changing cat litter.
While Salmonella or Campylobacter infection is unlikely to cause any problems with a pregnancy or with foetal development, it’s very unpleasant to suffer the effects during pregnancy. Pregnant women are advised to take steps to minimise the risk of infection: cooking eggs till the yolk and white are solid and avoiding products that may contain raw egg, such as homemade mayonnaise (shop bought mayonnaise is acceptable due to it not containing raw egg).
There are some other considerations for foods to avoid during pregnancy outlined below.
Liver and liver products contain high levels of vitamin A . Very high amounts of vitamin A (greater than 7000ug per day) may harm the developing fetus. Consequently, pregnant women are advised to avoid liver and liver products1.
As some vitamin supplements contain high levels of vitamin A, pregnant women need to be careful about which type of supplement they take. A woman who wants to take a multi-nutrient supplement should be directed towards those specially formulated for pregnancy. Fish liver oils also contain high levels of vitamin A and should be avoided during pregnancy.
There is no known safe alcohol intake in pregnancy therefore the Department of Health and the Food Safety Authority of Ireland recommend that pregnant women avoid alcohol completely.
Alcohol is a teratogen (a substance which is harmful to the developing foetus), and can easily pass through the placenta to the developing foetus. Alcohol consumption during pregnancy can lead to the development of Foetal Alcohol Syndrome which is characterised by behavioural problems, mental retardation, aggressiveness, nervousness, short attention span, growth retardation, and birth defects4. The negative effects of maternal alcohol consumption on a developing baby seem to occur at widely varying alcohol intakes. This makes it hard to justify a ‘safe’ alcohol intake during pregnancy1.
Concerns about high levels of mercury have led to a recommendation to avoid eating shark, swordfish and marlin during pregnancy. Mercury at high levels can damage the developing nervous system1.
Oysters and mussels should be completely avoided in pregnancy, as they may contain biotoxins which are not destroyed during cooking2.
Due the mercury content of tuna, pregnant women should limit their intake of tuna to one fresh tuna steak (150g) per week or two 240g tins of tuna per week1.
In the past, it was recommended that mothers of infants at high risk of developing atopic disease (infants with at least 1 first degree relative with an allergy) should avoid potentially high allergenic foods during pregnancy including eggs, cow’s milk, fish, peanuts, and tree nuts. However, the most recent guidelines by the Food Safety Authority of Ireland state that unless the mother is allergic to the food herself, there is no evidence to recommend the elimination of these foods from her diet1.
The Food Safety Authority of Ireland recommends that pregnant women should not have more than 200mg/day of coffee1 (approximately 2 cups of brewed coffee per day).