Foods to eatDuring pregnancy, the goal is to be eating nutritious foods most of the time, Krieger told Live Science. To maximize prenatal nutrition, she advises emphasizing the following five food groups: fruits, vegetables, lean protein, whole grains and dairy products. When counseling pregnant women, Krieger recommends they fill half their plates with fruits and vegetables, a quarter of it with whole grains and a quarter of it with a source of lean protein, and to also have a dairy product at every meal. Fruits and vegetables: Pregnant women should focus on fruits and vegetables, particularly during the second and third trimesters, Krieger said. Get between five and 10 "tennis ball"-size servings of produce every day, she said. These colorful foods are low in calories and filled with fiber, vitamins and minerals. Lean protein: Pregnant women should include good protein sources at every meal to support the baby's growth, such as meat, poultry, fish, eggs, beans, tofu, cheese, milk and nuts, Krieger said. Whole grains are an important source of energy in the diet, and they also provide fiber, iron and B-vitamins. At least half of a pregnant woman's carbohydrate choices each day should come from whole grains, such as oatmeal, whole-wheat pasta or breads and brown rice, Krieger said. Dairy: Aim for 3 to 4 servings of dairy foods a day, Krieger suggested, such as milk, yogurt and cheese, which provide good dietary sources of calcium, protein and vitamin D. In addition to a healthy diet, pregnant women also need a daily prenatal vitamin to obtain some of the nutrients that are hard to get from foods alone, such as folic acid and iron, according to ACOG. For women who take chewable prenatal vitamins, Krieger advised checking the product labels because chewables might not have sufficient iron levels in them.Foods to avoidAlcohol: Avoid alcohol during pregnancy, Krieger advised. Alcohol in the mother's blood can pass directly to the baby through the umbilical cord. Heavy use of alcohol during pregnancy has been linked with fetal alcohol spectrum disorders, a group of conditions that can include physical problems, as well as learning and behavioral difficulties in babies and children, according to the Centers for Disease Control and Prevention (CDC).Fish with high levels of mercury: Seafood such as swordfish, shark, king mackerel, and tilefish are high in levels of methyl mercury, according to the Academy of Nutrition and Dietetics, and should be avoided. Methyl mercury is a toxic chemical that can pass through the placenta and can be harmful to an unborn baby's developing brain, kidneys and nervous system. Unpasteurized food: According to the USDA, pregnant women are at high risk of getting sick from two different types of food poisoning: listeriosis, caused by the Listeriabacteria, and toxoplasmosis, an infection caused by a parasite.The CDC reports that Listeria infection may cause miscarriage, stillbirth, preterm labor, and illness or death in newborns. To avoid listeriosis, the USDA recommends forgoing the following foods during pregnancy: Unpasteurized (raw) milk and foods made from it, such as feta, Brie, Camembert, blue-veined cheeses, queso blanco and queso fresco. Pasteurization involves heating a product to a high temperature to kill harmful bacteria. Hot dogs, luncheon meats and cold cuts unless heated before eating to kill any bacteria. Store-bought deli salads, such as ham salad, chicken salad, tuna salad and seafood salad. Unpasteurized refrigerated meat spreads or pates.Raw meat: A mother can pass a Toxoplasma infection on to her baby, which can cause problems such as blindness and mental disability later in life, reports the CDC. To avoid toxoplasmosis, the USDA recommends avoiding the following foods during pregnancy: Rare, raw or undercooked meats and poultry. Raw fish, such as sushi, sashimi, ceviches and carpaccio.Raw and undercooked shellfish, such as clams, mussels, oysters and scallops.Some foods may increase a pregnant woman's risk for other types of food poisoning, including illness caused by salmonella and E. coli bacteria. Foodsafety.gov lists these foods to avoid during pregnancy, and why they pose a threat. Raw or undercooked eggs, such as soft-cooked, runny or poached eggs. Foods containing undercooked eggs, such as raw cookie dough or cake batter, tiramisu, chocolate mousse, homemade ice cream, homemade eggnog, Hollandaise sauce. Raw or undercooked sprouts, such as alfalfa, clover. Unpasteurized juice or cider.Pregnancy diet misconceptions:Morning sickness: When a mother-to-be is experiencing morning sickness, the biggest mistake she can make is thinking that if she doesn't eat, she'll feel better, Krieger said. The exact causes of morning sickness are not known, but it may be caused by hormonal changes or lower blood sugar, according to the Mayo Clinic. It can bring on waves of nausea and vomiting in some women, especially during the first three months of pregnancy. And "it's definitely not happening only in the morning," Krieger said. "It's any time of day." It's better to eat small amounts of foods that don't have an odor, since smells can also upset the stomach, she suggested.Food cravingsIt is common for women to develop a sudden urge or a strong dislike for a food during pregnancy. Some common cravings are for sweets, salty foods, red meat or fluids, Krieger said. Often, a craving is a body's way of saying it needs a specific nutrient, such as more protein or additional liquids to quench a thirst, rather than a particular food, she said. Eating for twoWhen people say that a pregnant woman is "eating for two," it doesn't mean she needs to consume twice as much food or double her calories." A woman is not eating for two during her first trimester," Krieger said. During the first three months, Krieger tells women that their calorie needs are basically the same as they were before pregnancy, because weight gain is recommended to be between 1 and 4 pounds in this early stage of pregnancy. Krieger typically advises pregnant women to add 200 calories to their usual dietary intake during the second trimester, and to add 300 calories during their third trimester when the baby is growing quickly. Weight gain during pregnancy, "Weight gain during pregnancy often has an ebb and a flow over the nine months," Krieger said. It's hard to measure where pregnancy weight is going, she said, adding that a scale does not reveal whether the pounds are going to a woman's body fat, baby weight or fluid gains. When it comes to pregnancy weight gain, Krieger advises mothers-to-be to look at the big picture: During regular prenatal checkups, focus on that the baby is growing normally rather than worrying about the number on a scale. The total number of calories needed per day during pregnancy depends on a woman's height, her weight before becoming pregnant, and how active she is on a daily basis. In general, underweight women need more calories during pregnancy; overweight and obese women need fewer of them. The Institute of Medicine (IOM) guidelines for total weight gain during a full-term pregnancy recommend that: Underweight women, who have a Body Mass Index (BMI) below 18.5, should gain 28 to 40 lbs. (12.7 to 18 kilograms). Normal weight women, who have a BMI of 18.5 to 24.9, should gain 25 to 35 lbs. (11.3 to 15.8 kg). Overweight women, who have a BMI of 25.0 to 29.9, should gain 15 to 25 lbs. (6.8 to 11.3 kg).Obese women, who have a BMI of 30.0 and above, should gain 11 to 20 lbs. (5 to 9 kg). Rate of weight gain: The IOM guidelines suggest that pregnant women gain between 1 and 4.5 lbs. (0.45 to 2 kg) total during their first trimester of pregnancy. The guidelines recommend that underweight and normal-weight women gain, on an average, about 1 pound every week during their second and third trimesters of pregnancy, and that overweight and obese women gain about half a pound every week in their second and third trimesters of pregnancy. Twins: The IOM guidelines for pregnancy weight gain when a woman is having twins are as follows:Normal weight: 37 to 54 lbs. (16.7 to 24.5 kg). Overweight: 31 to 50 lbs. (14 to 22.6 kg). Obese: 25 to 42 lbs. (11.3 to 19 kg). This article is for informational purposes only, and is not meant to offer medical advice.