Dietary guidelines for pregnancy: a review of current evidence.

In a successful pregnancy maternal health is maintained, a healthy baby is delivered and the mother is able to nurture her newborn adequately. Despite continued interest in the role and importance of maternal diet in this process, we do not have a clear understanding of how the nutritional status of the mother influences fetal growth and development. Recent epidemiological evidence of an association between poor fetal growth and adult disease highlights the need to reconsider the influences which act on the fetus, and the role maternal nutrition may play. Nutrient needs are increased in pregnancy. For the mother to be solely dependent upon her dietary intake to meet these demands, would represent a very high risk strategy. Hence adequate reserves are important for a successful outcome. Whilst there are numerous observational studies of diet during pregnancy, there are only limited data from well-controlled, randomised supplementation studies. A recent systematic review showed only dietary supplements balanced in energy and protein content to result consistently in improved fetal growth. There is no strong evidence that nutrient supplements confer benefit in women without overt deficiency. To interpret future dietary studies in pregnancy we need to consider metabolic differences between women which may influence their ability to meet fetal nutrient demand, to allow for nutrient-nutrient interactions, and to take account of differences in timing in gestation. Consideration of these factors in studies of pregnancy, will lead to a clearer understanding of the links between maternal diet and fetal growth and development. Until we have this understanding, it is reasonable to expect that women entering pregnancy are provided with a diet which is adequate, based upon our normal understanding of requirements, and it is not acceptable for women to be expected to carry a pregnancy with an obvious or overt nutritional deficiency.