Star volumes of villi and intervillous pores in placentae from low and high altitude pregnancies.

Histological sections of placentae from pregnancies completed at low altitude (400 m) and high altitude (3600 m) in Bolivia were analysed using a stereological estimator of the star volumes of villous 'domains' and intervillous 'pores'. The purpose was to test whether or not differences in the overall volumes of these compartments are accompanied by changes in their geometrical relationships. Whilst total placental volume did not vary with altitude, the total volume of villi declined by about 25% and total intervillous volume increased by 40% at high altitude. The star volume of villi also decreased by 25% (from 1.5 x 10(6) microns 3 at low altitude to 1.1 x 10(6) microns 3 at high altitude) whilst the star volume of intervillous pores increased 4-fold (from 87 x 10(6) microns 3 to 461 x 10(6) microns 3). These figures imply that villous domains decrease in size but may be constant in number. The most likely explanation is that villous trees at high altitude are scaled-down versions of their low-altitude counterparts. By contrast, although the intervillous pores enlarge they may decrease in number in the highland organ. This may reflect a change in the number of maternal cotyledons or in the spatial arrangement of villous trees.