Nutritional needs are increased during pregnancy and lactation for support of foetal and infant growth and development along with alterations in maternal tissues and metabolism. Total nutrient needs are not necessarily the sum of those accumulated in maternal tissues, products of pregnancy and lactation and those attributable to the maintenance of non-reproducing women. Maternal metabolism is adjusted through the elaboration of hormones that serve as mediators, redirecting nutrients to highly specialized maternal tissues specific to reproduction. It is most unlikely that heightened nutrient needs for successful reproduction can always be met from the maternal diet. Requirements for energy-yielding macronutrients increase modestly compared with several micronutrients that are unevenly distributed among foods. Altered nutrient utilization and mobilization of reserves often offset enhanced needs but sometimes nutrient deficiencies are precipitated by reproduction.

Source: Picciano, M.F. 2003. Pregnancy and lactation: Physiological adjustments, nutritional requirements and the role of dietary supplements. J. Nutr. 133: 1997S-2002S.