Good nutrition is a crucial step in having a healthy baby. A pregnancy takes about 300 extra calories a day to maintain, and an average-sized woman can expect to gain between 25 and 35 pounds overall. Those extra calories should be nutritious ones, however. A pregnant woman needs a balanced diet complete with protein, fruits, vegetables, and whole grains, and a minimum of sweets and fats.

"Good nutrition is extremely important even before a pregnancy," says Shirley Blakely, Ph.D., a registered dietitian with the Food and Drug Administration's Center for Food Safety and Applied Nutrition. "If nature favors the growing fetus, the mother will suffer if she hasn't had a good diet."

According to the March of Dimes, a pregnant woman should increase her daily food portions to include:

  • 6 to 11 servings of breads and other whole grains
  • 3 to 5 servings of vegetables
  • 2 to 4 servings of fruits
  • 4 to 6 servings of milk and milk products
  • 3 to 4 servings of meat and protein foods
  • 6 to 8 glasses of water, and no more than one soft drink or cup of coffee per day to limit caffeine.

Some nutrients have been found to provide specific benefit to mother or child. For example, the B vitamins have been found to be especially important. One of them, folate , or its synthetic form, folic acid , can reduce the risk of birth defects of the brain and spinal cord, called the "neural tube."

Each year, an estimated 2,500 babies are born with neural tube defects . The most common of these is spina bifida , in which the spine is not closed. The exposed nerves are damaged, leaving the child with varying degrees of paralysis, incontinence, and sometimes mental retardation. Because neural tube defects develop in the first 28 days after conception, "Once you know you're pregnant it's often too late to do anything about [them]," says Blakely.

Because half of all pregnancies are unplanned, the U.S. Public Health Service recommends that all women of childbearing age get 400 micrograms of folic acid each day. If all women received that amount daily, the incidence of neural tube defects might be reduced by an estimated 45 percent, studies suggest. To help reach this goal, FDA now requires that all flour products, such as breads, buns and bagels, be fortified with extra folic acid. Natural sources of folic acid include green leafy vegetables, nuts, beans, and citrus fruits. It's also in many fortified breakfast cereals and some vitamin supplements.

Calcium and iron are also especially important during pregnancy. Getting enough calcium will help prevent a new mother from losing her own bone density as the fetus uses the mineral for bone growth. Iron helps both the mother and baby's blood carry oxygen. Most women need supplements to maintain adequate levels of these minerals. A daily vitamin supplement, while not an adequate substitute for a healthy diet, helps fill in the gaps on days when a woman's diet is less than perfect.