Recent research published in the Archives of Pediatrics & Adolescent Medicine showed that a high-quality diet during pregnancy lowers the baby's risk of neural tube defects (such as spina bifida) and cleft lip and palate. Take a prenatal vitamin when you are trying to become pregnant and throughout the pregnancy. And eating a healthy diet is important.
A healthy diet should include (1) a variety of fruits and vegetables, (2) dairy and calcium-rich foods, (3) lean protein (lean meat, fish, eggs, tofu, beans, and peanut butter), (4) breads and grains, and (5) iron-rich foods (lean red meat, poultry, fish, breakfast cereals, nuts, and dried fruit).
Vitamins are important during pregnancy and these vitamin-rich foods help the babies growth and development: (1) Folic acid is a B vitamin that prevents the serious abnormalities of the brain and spinal cord called neural tube defects, including spina bifida. Cereals, leafy vegetables, and beans are all good sources of folic acid. (2) Vitamin C is in many foods, including oranges, grapefruit, strawberries, honeydew melon, papya, broccoli, cauliflower, green peppers, tomatoes, and brussel sprouts. (3) Vitamin D helps a baby have healthy bones and teeth. Good sources of vitamin D include fatty fish (salmon and tuna) and fortified milk or juice.
The Mayo Clinic's website has helpful information about this topic here.