Prenatal diagnosis of homozygous alpha-thalassemia-1 by cell-free fetal DNA in maternal plasma.

Objective: To investigate the use of cell-free fetal DNA (cff-DNA) to determine fetal status in pregnant women who were risk for having Hb Bart's.

Methods: Plasma DNA was extracted from 10 mL of maternal blood from couples who both were alpha-thalassemia-1 carriers (SEA deletion). Real time quantitative PCR was performed using fluorescence-labeled probes to monitor wild type (wt) and SEA allele. The quantity of each allele was determined by cycle threshold (Ct). ΔCt (Ct of wt- Ct of SEA) was calculated from each sample. Prenatal diagnosis was performed to determine fetal status.

Result: There were 62 Hb Bart's, 62 alpha-trait and 34 normal fetuses in this study. Mean ΔCt was 1.04 ± 0.38, 0.21 ± 0.37 and 0.14 ± 0.55 in Hb Bart's, alpha-trait and normal fetuses, respectively. Based on ROC, the best cut-off of ΔCt for predicting Hb Bart's was 0.51, giving 98.4% sensitivity and 20.8% false-positive rate. All but one Hb Bart's (98.4%) had ΔCt above 0.51, whereas 74.2% of alpha-trait and 88.2% of normal fetuses had ΔCt below 0.51.

Conclusion: There is a positive trend to use cff-DNA in maternal plasma for prenatal diagnosis of homozygous alpha-thalassemia-1. With this technique, invasive prenatal testing and complications can be avoided in 79.2% of unaffected fetuses.