Folic acid (from vitamin B) is one of the few nutrients known to prevent neural tube birth defects, such as spina bifida (a deformity of the spinal column), which affects 1 in every 1,000 babies born in the United States. The Centers for Disease Control reports that women who take the recommended daily dosage of folic acid in early pregnancy reduce their baby's risk of some birth defects by 50 percent. Folic acid is found naturally in orange juice, green leafy vegetables, and beans; however, it is difficult to obtain the recommended 400g daily through diet alone. So supplements that contain this B vitamin are recommended for pregnant women.
Ideally, you should get all your nutrients from natural foods. But during pregnancy, when there are so many cravings, food aversions, and morning sickness, a daily vitamin and mineral supplement is a good idea. Think of it as insurance against those days when you just can't take in enough of the foods your baby needs. Most often the supplement (usually referred to as prenatal vitamins) is prescribed by your doctor and contains all the nutrients you and your baby need. Women with special needs, such as those with diabetes or anemia, might need additional supplementation to meet their daily nutritional requirements.
When it comes to the amount of supplementation you need, follow your doctor's orders. More is not always better. An excess of certain nutrients can be harmful to your developing baby. Don't get caught up in the belief that if some is good, more must be better. Take only what your doctor prescribes.
Also be cautious about any herbal supplements or over-the-counter pills you might be taking. And talk to your doctor about any supplements you might be taking.