Obviously, drinking alcohol and doing drugs are the biggest no-no ...(in my opinion whether you're preggo or not! lol). There are a lot of foods doctors and books say you should avoid: processed meats (hot dogs, lunch meats) that aren't steamed/cooked, sushi and other kinds of fish (b/c of mercury levels), unpasteurized stuff (certain cheeses), and the list goes on and on. Also, no taking hot baths or getting in hot tubs or saunas that raise your core body temp.