An adequate supply of nutrients is probably the single most important environmental factor affecting pregnancy outcome. Women with early or closely spaced pregnancies are at increased risk of entering a reproductive cycle with reduced reserves. Maternal nutrient depletion may contribute to the increased incidence of preterm births and fetal growth retardation among these women as well as the increased risk of maternal mortality and morbidity. In the past, it was assumed that the fetus functioned as a parasite and withdrew its nutritional needs from maternal tissues. Studies in both animals and humans demonstrate, however, that if the maternal nutrient supply is inadequate, the delicate balance between maternal and fetal needs is disturbed and a state of biological competition exists. Furthermore, maternal nutritional status at conception influences how nutrients are partitioned between the mother and fetal dyad. In severe deficiencies maternal nutrition is given preference; in a marginal state the fetal compartment is favored. Although the studies of nutrient partitioning have focused on energy and protein, the partitioning of micronutrients may also be influenced by the maternal nutritional status. Marginal intakes of iron and folic acid during the reproductive period induce a poor maternal status for these nutrients during the interpregnancy interval. Poor iron and folic acid status has also been linked to preterm births and fetal growth retardation. Supplementation with food and micronutrients during the interpregnancy period may improve pregnancy outcomes and maternal health among women with early or closely spaced pregnancies.