Mathematical representation of organ growth in the human embryo/fetus.

During human pregnancy, there is a huge increase in the total weight of the embryo/fetus from conception to term. The total growth, which is the summation of growth of the various organs and tissues that make up the organism, was analyzed in a previous paper and fitted to the Gompertz equation for growth. In the present study, allometry, the quantitative representation of the consequence of size, was utilized to describe the correlation of individual fetal organ/tissue weights with the total fetal weight. The organ/tissue weight and the total fetal weight data used in the analyses were pooled from various sources that provided data ranging from 25 days to 300 days post-conception. Allometric equations are presented for 16 embryo/fetal organs and tissues. The standard allometric equation gave adequate fits for embryo/fetal adrenal, bone, bone marrow, brain, heart, liver, pancreas, plasma, skeletal muscle, extracellular water, thymus and thyroid; but it was necessary to use a quadratic form of the allometric equation for embryo/fetal fat, kidney, lung and spleen. Parameters were also calculated for crown-to-rump and crown-to-heels for fetal lengths that occur during pregnancy.