Histologie Study of Tritiated Thymidine Incorporation by Trophoblastic Villi in the First Trimester
With the recently introduced chorionic villi sampling techniques, the study of fetal chromosomes during the first trimester of pregnancy has become possible. After the biopsy has been performed, the length of time necessary to obtain suitable mitoses for karyotype analysis varies from a few hours with the direct technique (Simoni et al. 1983) to 10–21 days (mean, 16 days) with tissue cultures of macerated villi (Heaton et al. 1984). From the histologic point of view, a single villus of the first trimester shows a mesenchymal core, which is surrounded by a inner layer of cytotrophoblast and an outer layer of syncytiotrophoblast and ends with a dense cytotrophoblastic cell column (Boyd and Hamilton 1970). Dividing cells are observed in the mesenchymal core and the cytotrophoblast; to the contrary, the syncytiotrophoblast shows no mitoses. Shortly after biopsy, DNA synthesis, as demonstrated by tritiated thymidine incorporation, occurs in the cytotrophoblast and the villous core (Gerbie et al. 1968); this activity persists several days in vitro.
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