Performance and Utilization of Prenatal Screening Tests

Data from Ontario pregnancies are collected and analyzed on a regular basis to look at the utilization and performance of prenatal genetic screening tests. Refer to our most recent publications and program report for more information.

enhanced First Trimester Screening (eFTS) and Second Trimester Screening (STS) performance for singleton pregnancies*

Screening Modality	Chromosome Difference	Sensitivity (Detection Rate) % (95% CI)	Specificity % (95% CI)	False Positive Rate % (95% CI)
eFTS	Trisomy 21	88.23 (86.38, 89.91)	93.94 (93.87, 94.01)	6.06 (5.99, 6.13)
STS	Trisomy 21	87.18 (77.68, 93.68)^θ	91.38 (91.08, 91.68)^θ	8.62 (8.32, 8.92)^θ
eFTS	Trisomy 18	87.31 (83.61, 90.43)	99.71 (99.70, 99.73)	0.29 (0.27, 0.30)
STS	Trisomy 18	S (45.13, 86.14)^Ψ	99.38 (99.30, 99.46)	0.62 (0.54, 0.70)

Notes

Data were extracted from the BORN Information System (BIS) on 1 June, 2024, using cytogenetic testing data with results reported up to June 30, 2023. Note that data submission to the BIS is both voluntary and open to updates and amendments. This table represents a snapshot of the BIS on the date of data extraction.
The cohort timeline was defined by infant estimated date of delivery (EDD September 1, 2016 – March 31, 2023).
S = point estimate suppressed when confidence interval >20%.
θ = The cut-off for STS was changed on 1 April 2020 from 1 in 200 to 1 in 350. These performance metrics have been calculated with the current cut-off of 1 in 350 applied to the entire cohort to provide a stable estimate of the performance expected for this screen.
Ψ = performance data have a confidence interval greater than 20%. These performance metrics were calculated using small cell sizes from the available Multiple Marker Screening and cytogenetic data in the BIS and are subject to change as more data are collected. Please interpret these data with caution.
Only singleton pregnancies were included in this analysis.
Only pregnancies with a valid MMS result and cytogenetic result were included in this analysis. Outcome data were supplemented using clinical examination data from the BIS for negative results for T21, and 18 when cytogenetic results were missing.
"eFTS" includes both "4-marker eFTS" and "5-marker eFTS".

Detection rate = the proportion of pregnancies that are flagged as "screen positive" by this test and the baby really does have the chromosome difference.

Specificity = the proportion of pregnancies that get a "screen negative" result through this test and the baby does not have the chromosome difference.

False positive rate = the proportion of pregnancies that are flagged as "screen positive" but the baby does not really have the chromosome difference.

NIPT performance for singleton pregnancies with a screen from LifeLabs or Dynacare (publicly funded and private-pay)*

Chromosome Difference	Sensitivity (Detection Rate) % (95% CI)	Specificity % (95% CI)	False Positive Rate % (95% CI)	Positive Predictive Value % (95% CI)	Negative Predictive Value % (95% CI)
Trisomy 21	99.03 (98.41, 99.46)	99.94 (99.92, 99.95)	0.06 (0.05, 0.08)	96.06 (94.99, 96.96)	99.99 (99.98, 99.99)
Trisomy 18	95.99 (93.47, 97.74)	99.98 (99.97, 99.99)	0.02 (0.01, 0.03)	93.73 (90.82, 95.94)	99.99 (99.98, 99.99)
Trisomy 13	90.77 (84.43, 95.14)	99.96 (99.94, 99.97)	0.04 (0.03, 0.06)	73.29 (65.76, 79.95)	99.99 (99.98, 99.99)

NIPT performance for singleton pregnancies with a screen from LifeLabs or Dynacare (publicly funded only)*

Chromosome Difference	Sensitivity (Detection Rate) % (95% CI)	Specificity % (95% CI)	False Positive Rate % (95% CI)	Positive Predictive Value % (95% CI)	Negative Predictive Value % (95% CI)
Trisomy 21	99.13 (98.48, 99.55)	99.91 (99.89, 99.94)	0.09 (0.06, 0.11)	96.32 (95.20, 97.24)	99.98 (99.97, 99.99)
Trisomy 18	95.76 (92.98, 97.66)	99.97 (99.96, 99.99)	0.03 (0.01, 0.04)	95.18 (92.29, 97.22)	99.98 (99.96, 99.99)
Trisomy 13	92.52 (85.80, 96.72)	99.95 (99.93, 99.97)	0.05 (0.03, 0.07)	76.74 (68.49, 83.73)	99.99 (99.97, 99.99)

*Notes

Data were extracted from the BORN Information System (BIS) on 1 June, 2024, using cytogenetic testing data with results reported up to June 30, 2023. Note that data submission to the BIS is both voluntary and open to updates and amendments. This table represents a snapshot of the BIS on the date of data extraction.
The cohort timeline was defined by infant estimated date of delivery (EDD September 1, 2016 – March 31, 2023).
Only singleton pregnancies were included in this analysis.
Only pregnancies with a valid NIPT result and cytogenetic result were included in this analysis. Outcome data were supplemented using clinical examination data from the BIS for negative results for T21, and 18 when cytogenetic results were missing.

Detection rate = the proportion of pregnancies that are flagged as "high risk" by this test and the baby really does have the chromosome difference.

False positive rate = the proportion of pregnancies that this test will flag as "high risk" but the baby does not really have the chromosome difference.

Specificity = the proportion of pregnancies that get a "screen negative" result through this test and the baby does not have the chromosome difference.

Positive predictive value = what proportion of pregnancies with a "high risk" screening result do have the chromosome difference? A "high risk" result in a high-risk population (e.g. screen positive eFTS, ultrasound abnormalities) is more likely to be a true result than a "high risk" screening result in a low-risk population.

Negative predictive value = what proportion pregnancies with a "low risk" screening result truly do not have the chromosome difference?

Performance of Prenatal Screening System: The Basics

WHAT

WHY

WHO

HOW

The aim of this analysis was to measure the performance of Ontario's prenatal screening system for the detection of trisomy 21 and trisomy 18.

Evaluating real-world prenatal screening system performance is important for making improvements to the system, and facilitating decision making for pregnant individuals.

Singleton pregnancies with an estimated due date between September 1, 2016 and March 31, 2023 who underwent publicly funded and/or private-pay prenatal screening.

The analysis examined routinely collected data from BORN Ontario, the province's perinatal registry. BORN Ontario collects critical health data about every pregnancy, birth and newborn in Ontario.

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