In humans, plasma IGF-1 levels are barely detectable at birth, rise gradually during childhood, peak during mid-puberty until approximately 40 'tears of age, then decline gradually. Maternal plasma levels increase during pregnancy. In the diagnosis of growth disorders, measurements of IGF-1 are a useful indicator of growth hormone (GH) secretion. A normal plasma or serum IGF-1 concentration is strong evidence against GH deficiency. A low IGF-1 value implies GH deficiency and requires additional testing to determine whether GH secretion is subnormal. Measurement of IGF-1 is also useful in assessing change of nutritional status.