The amounts and deposition patterns of fibrin‐type fibrinoid at the villous surface are altered in pregnancy at high altitude

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In pregnancy at high altitude, there is preplacental (hypobaric) hypoxia and intrauterine fetal growth is restricted. Previous studies on placentas from Amerindian and nonindigenous women completing term pregnancies at low (LA; 400 m) and high (HA; 3600 m) altitudes in Bolivia showed that HA placentas had smaller surface areas of villi and smaller volumes of fibrin type fibrinoid (FTF). Recently we devised a stereological method for testing whether perivillous FTF (pFTF) is randomly distributed at the surface of villous trophoblast. Here the method is applied to test 2 experimental hypotheses: [1] deposition of pFTF is nonrandom regardless of altitude and [2] deposition patterns differ between altitudes. Uniform random samples of microscopical fields were drawn from Masson trichrome stained sections and intersection counts used to estimate the surface areas of, and patterns of pFTF on, 4 regions of trophoblast: nonsyncytial knots (nonSK), syncytial knots (SK), syncytial bridges (SB) and denudation sites (DEN). Absolute areas were compared by 2‐way analyses of variance. Expected and observed distributions were compared by (2 and contingency table analyses. At LA the mean (SEM) volume of FTF was 8.4 (1.54) cm3 and villous surface area was 7.0 (0.43) m2. At HA FTF volume was reduced by about 50% (P < 0.01) and villous surface by 20% (P < 0.01). The surface composition of trophoblast in LA placentas was nonSK (91%), SK (5%) and SB and DEN (both less than 3%). Relative surfaces were not significantly altered in HA placentas but, due to the impoverished growth of villi at HA, the changes represented a real decline in absolute surface of nonSK. At HA, the total surface of pFTF on trophoblast decreased by about 40%, from 4430 (564) cm2−2570 (406) cm2 (P < 0.01). At both altitudes pFTF deposition was preferentially found at DEN (12‐fold greater than expected for a random distribution). Pattern differences were detected between altitudes. In HA placentas the amount of pFTF deposited on nonSK regions was about 45% less (P < 0.05); apparent changes on SK and SB regions were not significant. These histometric findings suggest that the coagulation‐fibrinolysis steady state is altered at HA and favours greater fibrinolysis. At least some of the fibrinolytic or anticoagulant activity seems to reside in or on thinner regions of villous trophoblast and the placenta may be a relatively privileged site in terms of fibrinolysis. Also, reduced deposition of pFTF is probably linked to changes in the steady state of trophoblast turnover which seems to be perturbed in HA pregnancies.