Insulin-like growth factor binding proteins (BP) from human placenta are immunologically related to the growth hormone dependent binding protein in adult human serum (BP-53).

Preterm human placentae produce IGF-specific binding proteins. Placental binding proteins are immunologically similar to the growth hormone dependent binding protein in human serum (BP-53) and not the growth hormone independent binding protein (BP-28) in human serum and amniotic fluid. Placental production occurs in mesenchymal cells located in the villous core.