Trisomy 13 or 18 (mosaicism) in first trimester cytotrophoblast cells: false-positive results in 11 out of 51 cases

Objective: The finding of full or mosaic trisomy 13 or 18 in first trimester chorionic villus sampling (CVS) may be a false-positive result. This report provides incidence and outcome information that may be helpful in counselling individual patients and in choosing adequate follow-up. Study design: From a series of 6820 CVS cases, we retrospectively collected data on all patients (<F>n=51</F>) with full (<F>n=30</F>) or mosaic (<F>n=5</F>) trisomy 18, and full (<F>n=13</F>) or mosaic (<F>n=3</F>) trisomy 13 in cytotrophoblast cells. Results: Five false-positives were seen in patients with full trisomy 18 and three in the mosaic cases. One false-positive result was observed in full trisomy 13 and two false-positives in cases of mosaicism. No false-negative results were reported. Conclusion: The diagnosis of trisomy 13 or 18 in cytotrophoblasts should be confirmed in other tissues, unless fetal abnormalities are seen at ultrasound. In case of mosaicism, follow-up amniocentesis is advised. [Copyright &y& Elsevier]