While pregnant, it is always important to monitor the foods you are ingesting. Although listeriosis (a food-borne illness caused by ingesting the bacterium listeria) is not common, pregnant women are more apt to be affected by it than non-pregnant adults. This can be harmful to both the mother and the baby. In order to ensure the safety of you and your baby, it is recommended that deli meats be heated to a minimum of 160 degrees Fahrenheit before eating while pregnant.
http://www.americanpregnancy.org/pregnancycomplications/listeria.html