Your first prenatal checkup may not take place until you're well into the first trimester, yet this period is when crucial developmental milestones take place [source: Brundage]. Knowing this, you'll want to steer clear of potentially toxic ingredients. Many dangerous ingredients lurk in common foods. You'll want to avoid foods that could be contaminated with Listeria, a bacteria that can cross the placenta and cause miscarriage [source: U.S. Department of Agriculture]. Unless they are made from pasteurized milk, imported soft cheeses such as brie, camembert and feta are on this list. Raw eggs, fish, poultry, beef and pork shouldn't be ingested, either.
Staying away from raw meats usually isn't difficult for a pregnant, often queasy, woman. But when you're hit with a craving for sashimi or homemade ice cream (which often contains raw eggs), it can be easy to forget the risks [source: Harms]. Other foods, such as certain types of seafood, may contain high levels of mercury and should be eaten with rarity [source: March of Dimes: Avoid].
You should also avoid alcohol and cigarette smoke. Both substances cross the placenta and may cause harm [source: Kaiser Permanente]. Coffee consumption, however, gets mixed reviews. Although caffeine goes right into your baby's bloodstream, many women continue to drink coffee during pregnancy. In small amounts, caffeine appears to be OK. A 5-ounce cup of coffee has about 180 milligrams of caffeine, so a cup a day shouldn't cause too much concern [source: Organization of Teretology Information Specialists].