Should concurrent InSightŪ analysis be performed on late gestational age amniotic fluid specimens submitted for cytogenetic analysis?
Routine amniocentesis for cytogenetic analysis is generally performed on pregnancies between 14-18 weeks gestational age. Samples from third trimester pregnancies generally have a greater risk of culture failure. Percutaneous umbilical blood sampling (PUBS) has been used as an alternative to amniocentesis in the third trimester with success, but is technically difficult and carries a greater risk for adverse effects. Fluorescence in situ hybridization (FISH) for 13, 18, 21, X and Y (InSight) can potentially aid in rapid diagnosis of compromised specimens such as those obtained from late gestational age pregnancies.
Data from 25,918 amniotic fluid specimens received in 2005 at Genzyme Genetics was analyzed for culture failures resulting in no cytogenetic analyses. Overall failure rate was 0.17%. For the 1,097 third trimester studies, the failure rate was 0.82%, nearly 6 times the overall failure rate. Of the total failed cultures (45), 12 studies had concurrent InSight analysis which was informative in 10 cases (83%). Concurrent InSight analysis was ordered in 3 of 9 failed third trimester studies; all with informative results.
Chromosome abnormalities were detected in 6.93% of all successfully cultured amniotic fluid studies in 2005. However, 15.4% of third trimester amniotic studies had chromosome abnormalities. The likelihood of detecting a chromosome abnormality in the third trimester is more than twice as high, with a failure rate nearly six times as high, as routine amniotic fluid studies. InSight analysis, when standard cytogenetic analysis fails, would provide important clinical information without a second invasive procedure. Therefore, concurrent cytogenetic analysis and InSight would be beneficial in monitoring late gestational age pregnancies.
InSightŪ is a registered trademark of Genzyme Corporation