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.


METHODS
From a series of 6820 CVS cases, we retrospectively collected data on all patients (n=51) with full (n=30) or mosaic (n=5) trisomy 18, and full (n=13) or mosaic (n=3) 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.


CONCLUSIONS
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.
Schuring-Blom
G Heleen
GH
Department of Clinical Genetics, Academic Medical Centre, P.O. Box 22700, 1100 DE, Amsterdam, The Netherlands. g.h.schuring@amc.uva.nl
Boer
Kees
K
Knegt
Alida C
AC
Verjaal
Marjan
M
Leschot
Nico J
NJ
D000649:Amniocentesis; D015193:Chorionic Villi Sampling; D002882:Chromosomes, Human, Pair 13; D002887:Chromosomes, Human, Pair 18; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D009030:Mosaicism; D011247:Pregnancy; D011256:Pregnancy Outcome; D011261:Pregnancy Trimester, First; D012189:Retrospective Studies; D014314:Trisomy / Q000175:diagnosis*; D014327:Trophoblasts