Prenatal diagnosis from cystic hygroma fluid: The value of fluorescence insitu hybridization

OBJECTIVE: We sought to determine the optimal approach to the prenatal chro mosome analysis of cystic hygroma fluid using traditional cytogenetic analy sis and fluorescence in situ hybridization. STUDY DESIGN: A retrospective evaluation of our experience with traditional cytogenetic and fluorescence in situ hybridization analysis on cystic hygr oma fluid was performed through a systematic review of the Genzyme Genetics database from January 1995 to July 2000. Information on gestational age, s ample volume, clinical ultrasound findings (including fetal viability), cyt ogenetic results, fluorescence in situ hybridization results, and turn-arou nd-time were queried. RESULTS: Eighty-three specimens were included in the investigation. The mea n gestational age was 18.1 weeks (range, 13-27 weeks), and the mean sample volume was 207 mL (range, 0.1-101 mL). Of the 72 samples in which >5 mL of cystic hygroma fluid was available, the success rate for cytogenetic analys is was 76% (55/72 samples). In 11 specimens of less than or equal to5 mL of cystic hygroma fluid, cytogenetic analysis was successful in only 1 case ( 9%). Fluorescence in situ hybridization was attempted on 23 samples, 18 of which were successful (78%), including 6 of 9 cases of cell culture failure (67%). Both traditional cytogenetic analysis and fluorescence in situ hybr idization were performed in 21 instances when a sample of >5 mL was availab le. A successful result was obtained by either cytogenetic testing or fluor escence in situ hybridization analysis or both in 19 of 21 of these cases ( 90%). Samples of >5 mL from viable fetuses had a higher cytogenetio success rate (80%) and fluorescence in situ hybridization success rate (89%) than samples from fetuses with intrauterine death (38% and 50% cytogenetic and f luorescence in situ hybridization success rates, respectively.) The mean tu rn-around time was 8.2 days (range, 4-17 days). Results were available in l ess than or equal to 12 days in 91 % of cases. There was a 91 % aneuploidy rate identified, with 45,X occurring in 86% of the samples, CONCLUSION: We conclude that the optimal approach for the prenatal diagnosi s of chromosome abnormalities from cystic hygroma samples is to perform bot h traditional cytogenetic studies and interphase prenatal fluorescence in s itu hybridization evaluation for the most common aneuploidies that involve chromosomes 13, 18, 21, X, and Y. With this combined approach, our data ind icate that, in viable pregnancies with a fluid sample of >5 mL, a 90% diagn ostic success rate can be achieved.