Trace elements in human pregnancy
Recently there has been much interest in the effects of trace elements on the fetal growth and development and congenital defects. Baseline data on these trace elements are few and new more accurate methods for their analysis are being introduced. This study was designed to determine such baseline data. Methods were developed to determine zinc, copper, iron, manganese and chromium in serum and urine. A series of experiments were carried out to optimize the drying, charring, and atomizing parameters for each element in three different matrices: water, serum and urine. The method for chromium was hampered by the loss of the highly volatile chromium fraction and the analytical interference due to smoke and background absorption. The efficiency of the method was determined using three different methods: 1) a calibrated serum standard - Cation-cal; 2) serum samples analysed by method of additions; 3) serum analysed by flame atomic absorption. Serum zinc, copper, iron, manganese and chromium levels were measured in pregnant women at 6-10, 11-16, 24-26 weeks of gestation, at labor, and at 3 days and 6-30 weeks postpartum and in nonpregnant women. Trace elements in the venous, umbilical cord serum were also measured. The serum trace element levels in nonpregnant women were not influenced by the regular hormonal changes of the menstrual cycle. However, use of oral contraceptive agents resulted in a significant decline in serum chromium and increase in serum copper. In normal pregnancy, maternal serum zinc and chromium levels declined, serum copper rose and no changes were observed in serum iron and manganese levels. Iron supplementation eliminated any observable decline which would be expected in pregnancy. No statistically significant differences were observed between pathological and normal pregnancies, and due to lack of adequate numbers in each category, statistical analysis could not be done. However, the data seems to suggest that serum zinc and copper levels were decreased in women with threatened abortions. In some cases decreased copper levels may be observed in women who miscarry; or with premature rupture of membranes; or women who undergo induction of labor. A decline in serum iron levels, at term, was observed in prolonged gestation. Zinc, iron, manganese and chromium levels in the venous, umbilical cord serum were higher than the levels seen in maternal serum at term. Cord serum copper levels were only one-fourth of the maternal level at term. The fetus accumulates these trace elements from the mother for postnatal growth and development. Serum copper in the fetus is low because the fetus does not synthesize the major cuproenzyme, ceruloplasmin, until onset of postnatal life; however, it is known that fetal liver copper content is much higher than adult liver copper content, suggesting prenatal storage of the metal. Slightly lower serum zinc and iron levels were observed in low birthweight neonates and low serum iron was seen in postmature neonates.