[Amniotic fluid, amniocentesis, postmaturity].

The exchange among the elements of amniotic liquid is a dinamic process which keeps stable the concentration of their components, showing a variable relation with the maternal plasma in the differents stages of gestation. Thus the formations of the kidneys modifies the amniotic liquid with the urine excretion and then, factors as swallowing; the secretions of the skin and bronchi are factors which are implicated in its production. The amniocentesis is important in the study of high risk fetus, particulary with a prognostic value in the pregnancy sensitized to the Rh factor. The non cultivated celle give us information about the sexual chromatine and enzymes, to get a quick diagnosis, but this has to be confirmed with a culture cells for a final diagnosis, especially in diseases caused by inborn errors of metabolism.