Prenatal vitamins are used before and during pregnancy, and after for nursing mothers. A multivitamin and mineral supplement can help fill any nutritional needs that aren't being met by diet alone, and aid in a healthy pregnancy and fetal development.
Prenatal supplements can provide different vitamins and minerals than are available in a regular multivitamin, like folic acid and DHA, and typically include calcium and iron. Some women choose to take a separate combination of multivitamins and folic acid instead, which may be less expensive or more readily available over the counter.