Table 1. Number of fetal trisomy 13, 18 and 21 cases amongst 5967 CV samples with karyotypically normal results or low-level mosaicism <30% in STC-villi.

Chromosome aberration	Total number of trisomic cases	Number with normal STC	Number with mosaic STC<30%	Total number of normal or mosaic < 30% STC (%)
Trisomy 21	242	3	2	5 (2,0%)
Trisomy 18	123	6	3	9 (7.3%)
Trisomy 13	39	0	0	0
Total	404	9	5	14 (3,5%)