CA 125 in tissues and amniotic fluid during pregnancy.

CA 125 was assayed in amniotic fluid and tissue extracts by immunoradiometric assay, and immunohistochemical studies were performed on paraffin-embedded sections of endometrium, decidua, and fetal membranes with the monoclonal antibody OC 125 used as primary antibody. The concentration of CA 125 in amniotic fluid changes during pregnancy so that levels of 800 to 1000 U/ml are found before 12 weeks. Thereafter, levels of 4000 to 10,000 U/ml are detected routinely. As term approaches, amniotic fluid CA 125 concentrations fall to a range of 1000 to 2000 U/ml. Levels of CA 125 in tissue extracts of secretory endometrium and decidua were 65,000 and 29,500 U/gm of tissue, respectively. CA 125 was readily detected on the apical surfaces of glandular epithelium and in the secretions of endometrial glands obtained throughout the menstrual cycle. It was also detected in the lumina of decidualized glands throughout pregnancy. No antigen was detectable within glandular epithelial cells. We have previously reported high concentrations of CA 125 in chorionic tissue extracts (42,000 U/gm) and low concentrations in amniotic tissue extracts (275 U/gm). In contrast to those findings, immunohistochemical techniques detected CA 125 within the intercellular canaliculi that surround amniotic epithelial cells but not in chorion. We conclude that the likely source of amniotic fluid CA 125 is the decidua and that it gains access to the amniotic fluid via the intercellular canalicular system that traverses the amniotic epithelium.