Variations in expression of copper/zinc superoxide dismutase in villous trophoblast of the human placenta with gestational age

This study investigated expression of the key antioxidant enzyme copper/zinc superoxide dismutase in the villous trophoblast of the human placenta at different gestational ages from 8 weeks (last menstrual period) to term. Immunostaining for the enzyme was observed in the cytotrophoblast cells at all stages. Staining was generally absent from the syncytiotrophoblast at 8 weeks, except for small isolated areas close to the basal surface. The size and location of these areas suggested they were the result of recent cytotrophoblastic fusion. By 10 weeks, examples were more frequent and diffuse staining throughout most of the syncytiotrophoblast was observed at 12 weeks. The intensity of the immunostaining within the syncytiotrophoblast continued to increase until 14 weeks, by which time it matched generally that within the cytotrophoblast cells. A similar pattern of staining was observed within term material. These results are entirely consistent with the hypothesis that the oxygen tension within the intervillous space is low throughout the first trimester of pregnancy. They support the idea that an effective maternal circulation to the human placenta is only established at the start of the second trimester. (C) 1997 W. B. Saunders Company Ltd.