It’s often said that a pregnant woman must eat for two. Although that old adage doesn’t give a mother-to-be license to overeat, it does reflect the fact that she is responsible for her baby’s nutrition. The quality of her diet, good or bad, will have lasting effects on the health of her child, and eating well is one of a pregnant woman’s most essential responsibilities.

“Eating for two doesn’t mean eating twice as much,” said OB/GYN Dr. Kecia Gaither, “but a pregnant woman does need more calories, and getting those calories from healthy foods is more important than ever. Both mother and baby need foods that are packed with vitamins, minerals and other nutrients, not with empty calories from desserts, candy and soft drinks.”

A pregnant woman should eat well-balanced meals made up of a variety of foods that contain healthy amounts of proteins, carbohydrates, vitamins, minerals and fats. “Following a healthy diet is the best way to get the nutrients needed,” said Gaither. “For women who find it difficult to get enough of some nutrients in their diets, the doctor may prescribe prenatal vitamins or nutritional supplements to fill in the gaps and avoid deficiencies. Supplements may be particularly important for women who are vegetarians or have certain food allergies.”

Nutritional deficiencies can have serious consequences for the safety of the pregnancy and the health of the baby. And although all nutrients are important, some are more important than others and are more commonly deficient. Gaither highlighted those that are most critical:

Iron is needed to make hemoglobin, the protein in red blood cells that carries oxygen to all the tissues in the body and to the baby. Because the volume of blood expands during pregnancy, a woman needs twice her normal intake of iron to ensure a healthy supply of oxygen to the fetus and to support the development of the baby’s own blood supply. Iron deficiency may cause fatigue as well as complications such as premature delivery and low birth weight. Good sources of iron are lean meat, poultry and fish; leafy green vegetables; beans, nuts, raisins and dried fruits; and iron-fortified bread, cereal and pasta.

Folate/folic acid is an essential B vitamin that helps prevent defects such as spina bifida and abnormalities of the brain and spinal cord. Folate is a natural substance found in leafy green vegetables, citrus fruits and dried beans and peas. Folic acid is the synthetic form and is added to many foods, such as cereal, bread and pasta.

Calcium helps the baby develop strong bones and teeth and prevents the mother’s bones from weakening as calcium is leeched out of her bones and given to the baby. The best sources of calcium are dairy products, especially milk, cheese and yogurt, as well as broccoli and kale and calcium-fortified orange juice.

Vitamin D helps the body maintain proper levels of calcium and phosphorus and helps the baby’s bones and teeth grow. Insufficient vitamin D can cause abnormal bone growth and fractures in newborns. Good sources include fatty fish, such as salmon, and milk and cereal that has vitamin D added. Vitamin D is also made by the body from sunlight, but the dangers of overexposure to the sun make getting it from food a better idea.

DHA (docosahexaenoic acid) is a fat better known as omega-3 fatty acid that supports development of the baby’s brain. The best way to get it is by eating more fish, 8 to 12 ounces a week of low-mercury fish, such as salmon, herring, trout, anchovies and halibut. Orange juice, milk and eggs that have added DHA will be identified on the label.

Iodine is needed for the production of thyroid hormones, which increases by approximately 50 percent during pregnancy. Iodine also helps the baby’s brain and nervous system develop. Deficiency increases the risk of premature delivery and stillbirth. Good sources include fish, milk, cheese, yogurt, fortified cereal and bread and iodized salt.

Zinc is important throughout pregnancy to help the baby’s cells grow and replicate. In the early stages of pregnancy, inadequate zinc increases the risk of miscarriage. It can be found in lamb, beef, crabmeat, fortified cereals, nuts and beans.

Gaither concluded, “In general, a pregnant woman will need to consume an extra 300 calories a day chosen from fruits and vegetables, lean protein, whole grains and dairy products. What she eats is her baby’s source of nourishment, and by choosing wisely she can give her child the best opportunity for a healthy start in life.”

Kecia Gaither, M.D., MPH, FACOG, a perinatal consultant and women’s health expert, is a double board-certified physician in OB/GYN and Maternal-Fetal Medicine in New York City. Dr. Gaither is director of Perinatal Services at Lincoln Medical and Mental Health Center, a member of NYC Health + Hospitals System in Bronx, New York.