Prospective study of 22q11 deletion analysis in fetuses with excess nuchal translucency.

Abstract

The purpose of this study was to determine the frequency of 22q11 deletions (DiGeorge, velocardiofacial syndromes) in chromosomally normal fetuses with excess nuchal translucency. We evaluated chorionic villus sampling (CVS) samples submitted with an indication of excess nuchal translucency. If chromosome analysis was normal, permission was obtained to perform 22q11 microdeletion fluorescence in situ hybridization analysis. By Fisher exact test, the null hypothesis that there is no association between excess nuchal translucency and 22q11 deletions was tested. Among 239 CVS samples from fetuses with excess nuchal translucency, 93 (39%) were chromosomally abnormal. Of the remaining 146 specimens, 80 CVS samples were chromosomally normal, had documentation of nuchal translucency > 3.0 mm, and were included in the study at the referring obstetrician's request. None of the 80 fetuses with an increased nuchal translucency and normal karyotype demonstrated a 22q11 microdeletion. By Fisher exact test, the probability of 80 fetuses with excess nuchal translucency having no deletions of chromosome 22 was not significantly different than the expected rate of 0.18% (P value = 1). Routine 22q11 microdeletion analysis for fetuses with excess nuchal translucency is not indicated. Instead, we recommend storing an extra unbanded slide from the cultured CVS material to permit 22q11 FISH analysis should a cardiac malformation be identified later by fetal echocardiography.