Table 3. Details of trisomy 18 cases with normal or low-mosaic (<30%) results in STC-villi in our cohort of 5967 CV samples.
| Indication | Karyotype STC-villi (% +18) | FISH STC % +18 (N≥100 nuclei) | Karyotype LTC-villi | FISH LTC % +18 (N≥100 nuclei) | Confirmatory studies | |
|---|---|---|---|---|---|---|
| 1 | US: omphalocele, hygroma colli, hydrops foetalis; hydrothorax | 46,XX[8] (0%) | 0% | 47,XX,+18[14]/46,XX[2] | ~100%* | Skin: 100% metaphases (N = 61),and ~100%* interphase nuclei (N = 100) |
| 2 | US: IUGR | 46,XX[10] (0%) | 0% | 47,XX,+18[16] | ~100%* | Skin: ~100%* interphase nuclei (N = 100) |
| 3 | US: hydrops foetalis, cor vitium, abdominal wall defect | 46,XX[9] (0%) | 0% | 47,XX,+18[25] | --- | --- |
| 4 | US: NT 8 mm, IUGR | 47,XY,+18[3]/46,XY[18] (14%) | 0% | 47,XY,+18[9]/46,XY[1] | ~100%* | --- |
| 5 | US: omphalocele, NT 6 mm, ftCT 1:2 | 46,XX[10] (0%) | 0% | 47,XX,+18[9] | ~100%* | --- |
| 6 | US: hydrops foetalis, IUD | 46,XY[7] (0%) | 0% | 47,XY,+18[7]/46,XX[7] (MCC) | ~100%* (in Y-positive nuclei) | --- |
| 7 | US: hydrops foetalis, ascites, NT 7 mm | 46,XY[9] (0%) | 0% | 47,XY,+18[8]/47,XY,+2[10] | 38% +18 (and 32% +2) | AF: ~100%* interphase nuclei (N = 165) |
| 8 | US: encephalocele, IUGR | 48,XY,+mar,+18[1]/47,XY,+18[2]/47,XY,+mar[11]/46,XY[5] (16%) | FISH for mar identification: mar = der(18)(L1.84+, WCP18-) | 47,XY,+18[11] | ~100% * | Skin: ~100%* |
| 9 | US: hygroma colli | 47,XX,+18[2]/46,XX[18] (10%) | 0% | 47,XX,+18[16] | --- | --- |
US: ultrasound abnormalities; IUGR: intrauterine growth restriction; IUD: intrauterine death; NT: nuchal translucency; ftCT: abnormal first trimester screening results; AF: uncultured amniotic fluid cells; MCC: maternal cell contamination; STC-villi: short-term cultured villi; LTC-villi: long-term cultured villi
* The % of nuclei with 3 signals with probe L1.84 (18 centromere probe) varied between 70 and 100%, fitting a non-mosaic trisomy 18 according to our protocol.