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Table 2 Screening performance for trisomy 21 using contingent, reflex, and primary cfDNA screening strategies (assuming a screening population of 100,000 women, and eFTS used as the primary screening test for contingent and reflex cfDNA screening)

From: Prenatal screening for trisomy 21: a comparative performance and cost analysis of different screening strategies

Strategy Contingent cfDNA screening Reflex cfDNA screening Primary cfDNA screening
Risk cut-off(s) of eFTS 1 in 1000 1 in 1000 1 in 1000 1 in 50 and 1 in 1000  
cfDNA screening technology Sequencing Sequencing RCA/Imaging solution RCA/Imaging solution Sequencing RCA/Imaging solution
# eFTS positive 11,250 11,250 11,250 11,250 (a)
# cfDNA screening 11,250 11,250 11,250 9850 100,000 100,000
# cfDNA screening high risk 253 (b) 247 (c) 254 (c) 82 (c) 354 (b) 356 (c)
# cfDNA screening no-call result 135 (d) 371 (e) 56 (e) 49 (e) 1200 (d) 500 (e)
# patient receiving GC 11,250 (f) 618 (g) 311 (g) 1532 (h) 1554 (g) 856 (g)
# GC session 11,443 (i) 618 (g) 311 (g) 1532 (h) 1554 (g) 856 (g)
# PND (cfDNA screening high risk) 253 247 254 1482 (j) 354 356
# PND (cfDNA screening high risk/no-call) 388 618 311 1532 1554 856
# Expected T21 260 260 260 260 260 260
# T21 diagnosed through PND (cfDNA screening high risk) 242 236 243 246 (k) 254 256
# T21 diagnosed through PND (cfDNA screening high risk/no-call) 245 245 245 246 257 257
# T21 eFTS negative 13 13 13 13
# T21 cfDNA screening low risk 2 2 2 1 3 3
# T21 cfDNA screening no-call 3 8 1 0 3 1
# T21 missed by eFTS or cfDNA screening 15 15 15 14 3 3
# T21 livebirth 9 9 9 8 2 2
# Procedure related fetal loss 0 1 0 4 4 2
DR (cfDNA screening high risk) 92.2% 91.0% 93.6% 94.6% 97.7% 98.5%
FPR (cfDNA screening high risk) 0.01% 0.01% 0.01% 1.24% 0.10% 0.10%
Overall DR (all cfDNA screening no-call have a PND) 94.1% 94.1% 94.1% 94.7% 99.0% 99.0%
Overall FPR (all cfDNA screening no-call have a PND) 0.14% 0.37% 0.07% 1.29% 1.30% 0.60%
  1. Numbers of pregnancies were rounded to the nearest whole number
  2. T21 Trisomy 21, cfDNA screening cell free fetal DNA screening, eFTS Enhanced first trimester screening, RCA/Imaging solution automated high precision rolling circle amplification/Imaging solution, GC Genetic counselling, PND Prenatal diagnosis testing (Chorionic villus sampling and amniocentesis), DR Detection rate, FPR False positive rate
  3. a. Women with eFTS risk≥1/50 (1400) or risk between 1/51–1/1000 (9850); b. cfDNA screening high risk from the first and second tests; c. cfDNA screening high risk from the first test (assuming no repeat test is offered if the first test has a no-call result); d. cfDNA screening no-call result after the second test (assuming a repeat test is offered if the first test has no-call result); e: cfDNA screening no-call result after the first test; f: Women screen positive for eFTS; g: Women with cfDNA screening high risk or no-call results; h: Women with eFTS risk≥1 in 50 (1400) and women with high risk (82) or no-call cfDNA screening results (49); i: Women with positive eFTS (11,250) have a full session of GC, women with a high risk cfDNA screening (253) and no-call cfDNA screening (135) also have a follow-up 1/2 session of GC; j: Women with eFTS risk≥1 in 50 (1400) and high risk cfDNA screening (82); k: T21 diagnosed among women with eFTS risk≥1 in 50 or high risk cfDNA screening