Vitamins and minerals are, by definition, essential substances that are necessary for good health, and needed by every cell and organ to function appropriately. A deficiency of any one vitamin or mineral can be very serious. Although a very healthy diet rich in vegetables, fruits, and protein can provide sufficient amounts of most vitamins and minerals, many people do not consume an adequate diet. During pregnancy, there is an increased need for vitamins and minerals to promote a healthy pregnancy and a healthy baby. Prenatal supplements are intended to supplement a normal diet to ensure that adequate amounts of vitamins and minerals are consumed. The US Food and Drug Administration (FDA) has established Recommended Dietary Allowances for total vitamin/mineral intake from food and supplements, but they have not established recommendations for prenatal supplements. Therefore, there is a very wide variation in the content and quality of prenatal supplements. Many prenatal supplements contain only minimal levels of some vitamins and few or no minerals, in order to minimize cost and the number of pills. This results in insufficient vitamin/mineral supplementation for many women, and hence does not fully protect them or their children from pregnancy complications and health problems. Therefore, we have created our own set of recommendations for prenatal supplements. Our recommendations are based primarily on four sources: 1) FDA's Recommended Daily Allowances for pregnant women, which are estimated to meet the needs of 97.5% of healthy pregnant women. 2) FDA's Tolerable Upper Limit, which is the maximum amount of vitamins/minerals that can be safely consumed without any risk of health problems. 3) National Health and Nutrition Examination Survey (NHANES), which evaluates the average intake of vitamins and minerals by women ages 20-40 years in the US 4) Research studies on vitamin/mineral deficiencies or vitamin/mineral supplementation during pregnancy, and the effect on pregnancy, birth, and child health problems. In summary, the RDA establishes minimum recommended levels of vitamin/mineral intake from all sources, and the NHANES establishes the average intake from foods. The difference is what needs to be consumed in a supplement, on average. However, since people vary greatly in the quality of their diet, and since most vitamins and minerals have a high Tolerable Upper Limit, we generally recommend more than the difference between the RDA and the average NHANES. Vitamins generally have a larger Tolerable Upper Limit than do minerals. So, we recommend that prenatal vitamin/mineral supplements contain 100% of the RDA for most vitamins, and about 50% of the RDA for most minerals. However, based on additional research studies described below, in some cases we vary our recommendations from those averages.