Development of the early human placenta: a morphometric study.

The placentae of 46 normal pregnancies artificially terminated between 6 and 15 weeks of gestation were investigated morphologically to provide trends in early villous development. Study of the specimens included phase contrast microscopic examination and histomorphometric investigation in all cases, and scanning electron microscopy in ten cases. Histomorphometric measurements included the villous barrier thickness i.e. the distance between the intervillous space and the villous capillary lumen, the trophoblastic layer thickness and the volume fraction of each villous constituents, i.e. trophoblast, stroma and capillaries. Significant negative correlations were observed between gestational age and the villous barrier and trophoblastic thickness. The data obtained were separated into two groups, embryonic (5-10 weeks) and fetal (11-15 weeks) groups, and compared. The mean barrier thickness, the mean trophoblastic thickness, the mean volume fraction for trophoblast and the sprouting-villous index were significantly greater during the embryonic period compared with the fetal period. The mean volume fraction for the stroma and for the fetal capillaries, and the mean number of capillary profiles per villous profile were significantly smaller during the embryonic period than during the fetal period. The comparison of placental histomorphometric data obtained in cases of normal early pregnancies with those observed in cases of abnormal early pregnancies could help us to elucidate the origin of anatomical and biological changes in these cases.