NIPT detects fetal aneuploidy with high accuracy provided the cell-free DNA fetal fraction (FF) is sufficient. For samples not receiving a result, referral for discussion of invasive testing has been suggested as the most appropriate “next step.” Alternatively, precise estimation of the success rate of a redraw NIPT sample could allow a more comprehensive discussion of management options between provider and patient.METHODS:
We reviewed FF, maternal weight (MW), gestational age (GA), and the interval between draws (IBD) for 3,116 women whose initial single-nucleotide polymorphism (SNP)-based NIPT sample resulted in a no-call due to low FF and who submitted a second sample. Parameter correlations and redraw success rates were calculated.RESULTS:
The overall redraw success rate was 63.4%. Initial FF and IBD were positively correlated, MW inversely correlated, and GA not correlated with redraw success. The average increase in FF between draws was 1.2%. Women with initial FF below 2%, between 2% and 3%, and above 3% had redraw success rates of <30%, 55%, and >70%, respectively. Women with <200 or >200 pounds MW had 78.3% and 54.7% redraw success rates, respectively. Over the first three weeks, the redraw success rate increased by approximately 15% per week.CONCLUSION:
Women who do not receive a result on their SNP-based NIPT may have a good chance (>60%) for a successful redraw; further, waiting to redraw may increase the likelihood of redraw success. Women with high MW or especially low FF may benefit from referral for further evaluation and discussion of other options, including invasive testing.