Trace element needs in human pregnancy.

The importance of the trace metals zinc, copper and iron with respect to fetal growth in human pregnancy, with particular emphasis on their transfer to and uptake by the fetus, was discussed at a meeting of the Nutrition Society by Widdowson et al. (1974). The present paper examines the new information which is available in respect to the trace elements Zn, Cu, manganese, selenium and chromium. When considering the needs of human pregnancy there are several possible points in the maternal-fetal handling of nutrients where limitation could occur: (a) the maternal diet (i.e. the provision of nutrients), (b) maternal absorption from the diet, (c) maternal utero-placental blood flow (i.e. delivery of the nutrient), (d) placental transfer, (e) fetal uptake. Before looking at specific elements, there are some general considerations of maternal physiological adaptation to pregnancy which must be remembered. These include increased dietary absorption, of which there is some evidence for Fe (Heinrich et al. 1968; Apte & Iyengar, 1970; Svanberg, 1975); increased plasma volume which alters the concentrations of nutrients in the blood, e.g. folic acid (Hall et al. 1976); and increased urinary loss of nutrients because of increased renal blood flow and increased glomerular filtration rate such as occurs with amino acids (Hytten & Cheyne, 1972). In addition there are changes in the total number of erythrocytes and leucocytes with an alteration in the proportion of types of cells present (Letsky, 1980). There is also increase in maternal tissue protein (e.g. uterine muscle) and fetal tissue. Trace elements may be lost from the fetus into the amniotic fluid, but as gestation advances the fetal kidneys increasingly contribute to the volume of fluid, with consequent changes in the composition of the fluid (Lind et al. 1969). Some but not necessarily all nutrients thus ‘lost’ may be recycled by fetal swallowing.