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Table 1 Assumptions on prenatal screening for trisomy 21

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




 Number of pregnancies screened [17]



 Prevalence of T21 [19]



 Spontaneous fetal loss rate of T21 [20]



 Fetal loss rate after amnio/CVS [21]



 Median GA at eFTS (days)



Test performance

 eFTS risk cut-off

1 in 1000 (a)

1 in 50 and 1 in 51–1000 (b)

 eFTS DR [8]

95% (a)

67 and 28% (b)*

 eFTS FPR [8]

11% (a)

1 and 10% (b)*

 cfDNA screening DR [5, 6, 10]



 cfDNA screening FPR [5, 6, 10]



 cfDNA screening no-call result of 1st/2nd sample [5, 9]

3.3% /1.2% (c)

0.5%/NA (d)#

Turnaround time (days)

 Sample received at MMS lab to eFTS result issued



 Sample received at cfDNA screening lab to cfDNA screening result issued [22,23,24]

10 (c)

4 (d) +

 Positive eFTS, high risk or no-call cfDNA screening to GC



Cost (CAD)

 Unit cost of blood sample collection tube for cfDNA screening



 Unit cost of eFTS [17]



 Unit cost of cfDNA screening [ 22, 23]

$400 @


 Unit cost of GC

$250 ^


 Unit cost of CVS/amnio [17]


  1. T21 Trisomy 21, CVS Chorionic villus sampling, Amnio Amniocentesis, GA gestation age, eFTS Enhanced first trimester screening, DR Detection rate, FPR False positive rate, cfDNA screening cell free fetal DNA screening, RCA/Imaging solution automated high precision rolling circle amplification/Imaging solution, GC Genetic counselling, PND Prenatal diagnosis testing
  2. (a) One eFTS risk cut-off; (b) Two eFTS risk cut-offs; (c) Sequencing based cfDNA screening, (d) cfDNA screening using RCA/Imaging solution
  3. * Personal communication with Professor Howard Cuckle based on unpublished data from a study on eFTS performance for trisomy 21; # Round up from 0.28%; + Personal communication with Professor Geralyn Messerlian; @ The cost of a basic cfDNA test to self-paid patients after considering possible future price drop for both sequencing and RCA/Imaging based tests; ^ Estimated from Physician Services Under the Health Insurance Act, Schedule of Benefits (Page A67), Ministry of Health and Long-term Care, December 22, 2015