A stereological method for testing whether or not there is random deposition of perivillous fibrin-type fibrinoid at the villous surface: Description and pilot applications to term placentae

We present a stereological method for testing whether or not there is random deposition of fibrin-type fibrinoid (FTF) at the villous surface of human placenta. The method requires random sampling of tissue with test lattice lines superimposed on microscopic fields at random positions and orientations. Test lines are used to generate chance intersections with specified sub-domains of the villous surface. At least three sub-domains are distinguishable: non-syncytial knots (nonSK), syncytial knots (SK) and areas of trophoblast de-epithelialization (DEP). Other sub-domains may be included to suit: individual circumstances and project aims. The relative numbers of intersections with sub-domains provide the basis for an 'expected' distribution. Subsequently, this is compared with an 'observed' distribution which can be calculated from empirical estimates of the numbers of intersections with sub-domains associated with perivillous FTF (e.g. nonSK + FTF, SK + FTF and DEP + FTF). Expected and observed distributions can be compared by a chi-squared analysis. If the null hypothesis (no difference) is rejected, chi-squared values for individual sub-domains can be analysed in order to localize and interpret sites of preferential deposition. Comparisons may be drawn for individual placentae as well as a group of placentae, thereby permitting assessment of inter-placental variability. Finally between-group comparisons may be drawn in order to test whether or not FTF deposition patterns differ in control and other pregnancies. Worked examples of the statistical procedures are provided. Preliminary results of applications to placentae from normal and complicated (hypobaric hypoxia) pregnancies are presented. They show that FTF deposition is non-random and preferentially located at sites of de-epithelialization. De-epithelialization may be a consequence of syncytial degeneration but also, at least in part, of continuous trophoblast turnover in which syncytial fragments rich in (pre-) apoprotic nuclei detach from the epithelium and are deported from the maternal intervillous space. The nascent detachment site is immediately covered by FTF prior to repair by re-epithelialization. (C) 2000 Harcourt Publishers Ltd.