Chemical Development in utero

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Abstract
13 immature fetuses and 6 stillborn infants weighing more than 3 kg. were studied along with the placentae of 12 of the fetuses and infants. The fetus begins to lay down fat when it weighs 800-1000 g., and by the time it weighs 3000 g. the amt. of fat in its body is approx. equal to the amt. of protein (12%). After this the fat increases more rapidly than the protein; one stillborn infant which weighed 4375 g. contained 28% of fat. The concn. of Na/100 g. of fat-free body tissue decreased until the fetal wt. was about 2000 g., and then remained constant until term. The value reached was the same as in adult life. The concn. of K in the fat-free body tissue increased throughout intrauterine life, but the concn. in the whole body altered little from the time the fetus began to lay down fat. The concn. of C and P increased with increasing wt., so that the percentage of C at full-term was more than twice and of P a little less than twice as high as it was in the fetuses weighing 200-300 g. The percentage of Fe and Cu in the fetus increased with development while that of Zn did not change. The liver and spleen contained about 50% of the Cu, 25% of the Zn, and 1/8 of the Fe in the whole body. The concn. of I in the thyroid appeared to increase during fetal life and after, and in the thyroids from 3 adults was about 20 times as high in those from the immature fetuses. At the 17-19th week of pregnancy, the fetus and its placenta were of approx. equal wt., and contained similar amts. of N, fat, and K. During the last 4 mos. the fetus grows much more rapidly so that at full-term it weighed 5 or 6 times as much as its placenta. The "concn." of N and K were similar in both, but those of fat, C, Mg, P, Cu, and Zn were all higher in the fetus than in its placenta.
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