Cacheris, Phillip Michael

Abstract Background Noninvasive prenatal screening for common autosomal trisomies, sex chromosome aneuploidies and microdeletions vary by methodology and laboratory practice. The fetal portion of all cell-free DNA in the maternal circulation defines the fetal fraction (FF). The minimum specimen FF levels for reporting results vary between laboratories as well as the screening target (e.g., common trisomies vs select microdeletions). This variability can lead to confusion for both healthcare providers and patients. Methods Participants in the College of American Pathologists Non-Invasive Prenatal Testing 2021-B Exercise provided FF estimates for 3 manufactured samples. Responses to supplemental questions were also collected and analyzed. Results Overall, 72 of 77 participants responded. FF was measured by 66 participants using sequence counts (40), single nucleotide polymorphisms (15), fragment length (24), and Y chromosome sequences (24). Nearly half (48%) used multiple methods. For common trisomies, minimum FFs were none or <1% (n = 7), 1.0% to 3.9% (n = 35), 4.0% to 6.9% (n = 23), and ≥7.0% (n = 1); 4 participants did not measure FF. Challenge-specific FFs were variable with CVs of 13%, 15%, and 36%; the latter rate appears due to that sample’s fetal karyotype of 47,XYY. Comparing adjusted FF results for the 3 samples shows that 85% of participant results were within 20% of the consensus. Conclusions Using multiple methods to estimate FF was common, and cutoff levels for sample suitability varied widely. Within-laboratory FFs were less variable than between laboratories. Current FF estimates from clinical laboratories are not standardized and should be considered laboratory-specific.

AbstractObjectiveDetermine current analytical methods and number of cell‐free (cf) DNA prenatal screening tests performed for common trisomies.MethodsThe College of American Pathologists 2022‐B Noninvasive Prenatal Testing exercise was distributed in December 2022 to 93 participants in 22 countries. Supplemental questions included the number of tests performed in a recent month and the proportion of samples originating outside the United States (US).ResultsEighty‐three participants from three continents returned results; 74 (89%) were suitable for the analyses. Nine manufacturer/platform combinations were identified, most commonly Illumina/Nextseq (55%). The most common methodology was whole genome sequencing (76%). Annualized cfDNA tests were 2.80 million, with Asian, European and North American participants representing 10.6%, 6.5% and 82.9% of tests, respectively. When restricted to US in‐country tests, the annualized rate was 2.18 million, with four of 20 participants testing 79.2%. Among 73 respondents, 63 (86%) were for‐profit, eight (11%) were non‐profit academic or government supported and the remaining two included hospital‐based and private non‐profit. Eighteen (25%) supported relevant academic training.ConclusionIn 2011, screening for common trisomies was based on serum/ultrasound markers with an estimated 2.96 million US pregnancies screened in 131 laboratories. In 2022, cfDNA‐based screening was offered by 20 laboratories testing 2.18 million US pregnancies.