The problem with luncheon or deli meat is that it could potentially carry listeria, a bacterium that can wind up in processed meats (including deli meats and hot dogs) sometime between the cooking and packaging processes. Listeriosis causes serious illness in about 2,500 Americans each year. The Center for Disease Control and Prevention estimates that pregnant women, who make up about 30 percent of those listeriosis cases, are about 20 times more likely to contract the disease than healthy non-pregnant people. Though the infection may not feel much worse than the flu, it can lead to miscarriage, premature delivery or stillbirth, and can also spread to baby.
To play it safe, reheat all deli meat to at least 165 degrees before chowing down, or go for other sandwiches at lunch, like grilled chicken or tuna.