A longitudinal study on plasma somatomedin activity in full-term, preterm and small-for-gestational age newborns.

Plasma somatomedin (SM) activity was measured longitudinally in the first days of life by Van den Brande bioassay in 10 term, 8 premature and 5 small-for-date newborns. Other term, premature and small-for-date newborns were assayed between the 4th and 8th days by a cross-sectional-type study. A very significant increase in SM activity was observed in term newborns on the 3rd day lasting for about a week, when values usually observed in young children were reached. In premature and small-for-date newborns such an increase was not present but rather a slight decrease on the 3rd day was observed. The presence of a circulating inhibitory substance in the plasma of premature and small-for-date newborns with undetectable SM activity was shown.