Rapid aneuploidy testing versus traditional karyotyping in amniocentesis for certain referral indications.

Objective: (1) To determine the suitability of replacing full karyotype analysis with quantitative fluorescent polymerase chain reaction (QF-PCR) for prenatal diagnosis in amniotic fluid samples obtained by amniocentesis. (2) To evaluate an indication-based classification of cases at risk of missing clinically relevant chromosomal disorders by QF-PCR.

Methods: We reviewed all fetal karyotypes obtained by amniocentesis between January 2004 and December 2008. We compared the cytogenetic findings obtained through conventional karyotype with those that would have been theoretically obtained using QF-PCR.

Results: Of the 4007 karyotypes obtained, 110 abnormal karyotypes were found (2.8%). Out of these, 30 (27%) were chromosomal abnormalities (CA) which would not have been detected by PCR alone. These included 16 cases (53%) predicted to confer no increased risk, 9 (30%) predicted to have a low risk, and 5 (17%) with an uncertain or high risk of fetal abnormality. A policy of QF-PCR alone would have identified 80 of 85 (94%) clinically significant CA. When QF-PCR shows a normal result, the overall residual risk is 0.75% for any CA and 0.12% for a clinical significant CA.

Conclusion: In our population, a policy of QF-PCR alone would miss 0.12% clinically relevant CA. QF-PCR directed to common aneuploidies can be considered as an economically and clinically acceptable prenatal diagnosis policy, offering full karyotype only for specific indications.