Objective:To estimate the in vivo dimensions of the fetal villous tree of the normal term placenta.
Methods:Dual-circuit perfusion-fixation of a cotyledon from eight normal term placentas was performed with random intra-cotyledon tissue sampling. Stereologic methods were used to derive estimates of villous (intermediate and terminal) surface area and volume, and star volume (a measure of villous volume).
Results:Villous surface area (mean 20.9 m2 [standard deviation 1.8]), capillary surface area (12.8 m2 [1.5]), villous volume (469 mL [40]), and capillary volume (80 mL [10]) values were all approximately 50% higher than reported previously. Star volume estimates ranged from 480 to 1350 μm3.
Conclusion:Tissue perfusion-fixation more accurately reconstructs the in vivo state, resulting in higher reference values than previously thought for the fetal villous tree dimensions. Up to one-quarter of fetoplacental blood volume is likely to be accommodated within the placenta at term.
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