Prolactin in normal pregnancy: relationship of maternal, fetal, and amniotic fluid levels.

Serum prolactin was measured simultaneously by a homologous radioimmunoassay in 92 parturients and their offspring at term, and in maternal serum and amniotic fluid during various stages of normal pregnancy. Serum levels of 208 +/- 8 ng. per millilter were found in maternal blood; the corresponding levels in the cord serum were 354 +/- 14 ng. per milliliter. Prolactin levels in amniotic fluid were found to be 2- to 10-fold higher than the corresponding levels of the mothers. The possible source of the amniotic fluid prolactin molecule, which is identical with the human pituitary molecule, is discussed.