We have studied chorionic villi from 38 placentae obtained from spontaneous abortions at 7 to 12 weeks of pregnancy. Samples were separated into four groups: (1) early normal (7-9 weeks of pregnancy, normal karyotype); (2) late normal (10-12 weeks of pregnancy, normal karyotype); (3) early trisomic (7-9 weeks of pregnancy, trisomy 16 karyotype); and (4) late trisomic (10-12 weeks of pregnancy, trisomy 16 karyotype). Villous area trophoblastic area, stromal area and cell density were analysed through morphometric studies in serial sections. These were stained with haematoxylin-eosin-Alcian blue, picrosirius and diastase-periodic acid Schiff techniques. Early trisomic villi were not overtly different from normal karyotype villi. In contrast, late trisomy 16 chorionic villi had a smaller area, and the chorionic mesenchyme showed lower collagen and cell density. The morphological differences in villi described here could suggest an inability to maintain normal rates of proliferation and m
