CBS News Medical Correspondent Dr. Jennifer Ashton, a practicing OB-GYN, said on "The Early Show" pregnant women should have a well-rounded nutritious diet. But in that diet, they shouldn't eat certain foods that may harm the baby.
One of those foods is cooked seafood high in mercury. Ashton explained the bigger and older the fish, the more mercury it may contain.
According to Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) guidelines, women should avoid swordfish, shark, king mackerel and tilefish during their pregnancies.
The same goes for raw seafood.
Ashton said, "It's especially important to avoid oysters and clams because of the harmful bacteria or viruses. Avoid smoked seafood, such as lox. Cook seafood properly -- make sure fish is opaque."
Women should also avoid undercooked meat, poultry, and eggs.
"During pregnancy, changes in your metabolism and circulation may increase the risk of bacterial food poisoning," Ashton said. "Your reaction may be more severe than if you weren't pregnant. Rarely, your baby may get sick, too."
Unpasteurized foods may also be a danger to pregnant women.
"Many low-fat dairy products, such as skim milk, mozzarella cheese and cottage cheese, can be a healthy part of your diet," Ashton said. "But anything containing unpasteurized milk is a no-no. These products may lead to food-borne illness."
Soft cheeses are an example of a potential risk. Unless they are clearly labeled as being made with pasteurized milk, Ashton said pregnant women shouldn't eat brie, feta, camembert and blue cheese.
And drinking that eighth cup of coffee when you're pregnant may also not be the best idea, as excess caffeine has potential to harm your unborn baby.
Ashton said, "Caffeine can cross the placenta and affect your baby's heart rate. Some studies suggest that drinking too much caffeine may be associated with a small decrease in birth weight or an increased risk of miscarriage and stillbirth. In fact, a large 2008 study suggests that 200 milligrams of caffeine a day -- about a 12-ounce cup of brewed coffee -- during pregnancy may slow fetal growth."
Ashton said health care providers may recommend limiting the amount of caffeine in your diet to less than 200 milligrams a day during pregnancy to avoid this potential risk.
Passing on alcohol is also an important thing to remember during pregnancy. Ashton said one drink isn't likely to hurt your baby, but no level of alcohol has been proved safe during pregnancy.
"The safest bet is to avoid alcohol entirely," she said. "Consider the risks. Mothers who drink alcohol have a higher risk of miscarriage and stillbirth. Too much alcohol during pregnancy may result in fetal alcohol syndrome, which can cause facial deformities, heart problems, low birth weight and mental retardation. Even moderate drinking can impact your baby's brain development."
Many women experience cravings for certain foods when they're expecting. But is there a health-related reason why this occurs?
Referring to WebMD, Ashton said food cravings during pregnancy are normal, although there is no widely accepted explanation for why they occur. According to WebMD, almost two-thirds of all pregnant women have some type of food craving.
She said, "If you develop a sudden urge for a certain food, go ahead and indulge your craving if it provides energy or an essential nutrient. But, if your craving persists and prevents you from getting other essential nutrients in your diet, try to create more of a balance in your daily diet during pregnancy."
Ashton pointed out that during pregnancy, your taste for certain foods may change.
"You may suddenly dislike foods you were fond of before you became pregnant," she said. "Some women feel strong urges to eat non-food items such as ice, laundry starch, dirt, clay, chalk, ashes, or paint chips. This is called pica, and it may be associated with an iron deficiency, such as anemia. Do not give in to these non-food cravings. They can be harmful to both you and your baby. Tell your health care provider if you have these non-food cravings."
Ashton added, if you have any problems that prevent you from eating balanced meals and gaining weight properly, ask you health care provider for advice. She said registered dietitians -- the nutrition experts -- are available to help you maintain good nutrition throughout your pregnancy.
As forgetting back in shape after pregnancy, Ashton said the key to weight control is a blend of good eating habits and regular exercise.
"Eat foods that are rich in nutrients, but low in calories. Choose exercise that you like, and vary it to get an overall workout," she said. "Talk to your doctor. He or she may suggest ways to help you lose weight and maintain a healthy weight."
Also, "Early Show" co-anchor Maggie Rodriguez spoke with four expectant mothers about their pregnancies and how they're coping with the changes they're experiencing. To hear their stories, click on the video below.
Watch CBS News Videos Online