Prenatal Screening Ontario Study


Ottawa, Ontario — Wednesday August 4, 2021


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population-based study examining routinely collected data from BORN Ontario, the province’s perinatal registry.


Measure the performance and impact of Ontario’s prenatal screening system for aneuploidy after the incorporation of cfDNA testing, also known as NIPT (which measures placental DNA circulating in the blood of the pregnant person).


In Ontario, pregnant individuals are offered publicly funded multiple marker screening (which includes measuring hormones from the blood, and other information). Publicly funded cfDNA screening is available to those with an increased chance of having a pregnancy with certain aneuploidies, like trisomy 21 (Down syndrome) or trisomy 18.


Data from 373,682 singleton pregnancies with a due date between Sept 1, 2016 and March 31, 2019, that were offered publicly funded prenatal screening.


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

Key findings

  • Prenatal screening is a choice. The offer of prenatal screening was accepted for 69.9% of all singleton pregnancies
  • 2.4% of all screened pregnancies underwent prenatal diagnosis. There was nearly a twofold decrease in prenatal diagnosis since the introduction of cfDNA screening.
  • The overall sensitivity of prenatal screening for trisomy 21 was 89.9%.  The overall sensitivity of prenatal screening for trisomy 18 was 80.5%
  • The overall sensitivity of prenatal screening for trisomy 21 was 98.8%.  The overall sensitivity of prenatal screening for trisomy 18 was 99.9%.
  • Sensitivity refers to the proportion of pregnancies with trisomy 21 / trisomy 18 that received positive screening results.
  • Specificity refers to the proportion of pregnancies without trisomy 21 / trisomy 18 that received negative screening results.
  • 65.2% of pregnancies with a screen positive cfDNA result had invasive prenatal diagnostic testing. Pregnant people continue to make individual decisions about prenatal testing.


This study demonstrates that pregnant Ontarians have access to a robust, high-quality prenatal screening system that reduces invasive prenatal diagnostic testing and supports informed decision making.


Dougan SD, Okun N, Bellai-Dussault K et al. Performance of a universally offered prenatal screening program incorporating cfDNA in Ontario, Canada: a descriptive population-based cohort study of 280,000 pregnancies,CMAJ2021. DOI:

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