Statistical comparisons indicate that within 12 hours of birth the serum protein-bound iodine of the infant is of the same order of magnitude, on the average, as that present in maternal blood during pregnancy or within a few hours of delivery. During the remainder of the first week of life there occurs a transient statistically significant increase in the mean value of this iodine fraction. During the sixth to twelfth week the concentrations fall below those present neonatally, but at this time or at any subsequent age up to 1 year, they are still on the average above those encountered in euthyroid nonpregnant adults or in older children. The possible relationship of these higher mean values in infancy to increased thyroid function in the rapidly growing infant have been mentioned with emphasis on the elevated concentration of circulating thyroxin.
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