The detection of chromosome anomalies by QF-PCR and residual risks as compared to G-banded analysis.

Objective: To determine the detection rate of clinically significant chromosome abnormalities using quantitative fluorescent polymerase chain reaction (QF-PCR) of fetal DNA in comparison with G-banded analysis of cultured amniotic fluid cells and determine the residual risk if QF-PCR were performed alone for low-risk cases.

Methods: Amniotic fluid samples were prospectively categorized based on the likelihood of the fetus having a chromosome anomaly. QF-PCR results were compared with the G-banded findings. The distribution of patients and the rates of clinically significant anomalies in each risk category were determined.

Results: A total of 4176 amniotic fluid samples were studied. Among these, 331 cases with abnormalities were detected by both methods and an additional 19 abnormal cases were detected by G-banding only. Five of those undetected by QF-PCR were considered clinically significant, four of which were referred due to an elevated a priori risk (>4%). If QF-PCR is performed in all cases and G-banding performed only in higher risk cases, the residual risk for a clinically significant chromosome abnormality will be as low as 0.083%.

Conclusions: This study suggests that QF-PCR alone is appropriate for patients with uncomplicated pregnancies, who are referred solely for an increased risk of a common trisomy.