Prenatal cell-free DNA screening test failures: a systematic review of failure rates, risks of Down syndrome, and impact of repeat testing

Purpose: We systematically reviewed the published literature on test failure rates for the sequencing of cell-free DNA (cfDNA) in maternal plasma to identify Down syndrome. Methods: We searched peer-reviewed English publications with diagnostic results on all pregnancies that provided test failure rates. Data on the odds of failure in Down syndrome and euploid pregnancies and the impact of repeat testing were extracted. Random-effects modeling was then used to identify moderators that could explain variability. Results: Thirty articles satisfied the inclusion criteria for overall failure rates. Study location (Western and Asian with initial testing, and Western with repeat testing) were significant moderators with failure rates of 3.3, 0.6, and 1.2%, respectively (P = 0.001). The odds ratio for Down syndrome in successful versus failed tests was 0.98 (95% confidence interval: 0.62-1.55, I-2 = 0%). Repeat testing from 14 large clinical cohort studies found that 83% (range: 52-100%) of failures were repeated, with 79% (range: 46-97%) being successful. Conclusion: Lower failure rates in Asian studies may be related to not routinely measuring the fetal fraction and to fewer obese women. Repeat cfDNA testing is effective in providing reliable results after initial failures. Protocols for primary cfDNA screening should focus on Down syndrome, with less common and more structurally abnormal trisomy 18 and 13 pregnancies treated as adjuncts.