PRENATAL-DIAGNOSIS BY IN-SITU HYBRIDIZATION ON UNCULTURED AMNIOCYTES - REDUCED SENSITIVITY AND POTENTIAL RISK OF MISDIAGNOSIS IN BLOOD-STAINED SAMPLES

Maternal cell contamination was assessed in 18 macroscopically blood-s tained amniotic fluid samples from male fetuses. The samples were anal ysed by double-target fluorescent in situ hybridization (ISH) with Y a nd X chromosome-specific probes. The only sample with an aberrant kary otype (47,XY, +18) was also analysed by hybridization with a chromosom e 18-specific probe. An interpretation of extensive maternal cell cont amination was made in two samples, one of which was the sample with tr isomy 18. ISH with the chromosome 18-specific probe on this latter sam ple showed that the sensitivity of the ISH method for chromosome enume ration of uncultured amniotic fluid samples may be reduced in blood-st ained samples. It was calculated that by using ISH for chromosome enum eration of the two extensively contaminated samples, a case of trisomy 21 might have been overlooked in both samples, while a case of trisom y 18 might only have been overlooked in one of the samples. It is conc luded that ISH should not be used for chromosome enumeration of uncult ured amniotic fluid samples that are macroscopically blood-stained wit hout further technical developments.