The Impact of COVID-19 on Prenatal Screening

What were the anticipated effects of the COVID-19 pandemic on prenatal screening?

The COVID-19 pandemic was anticipated to have an effect on how prenatal screening services in Ontario were delivered, particularly with respect to patient access to nuchal translucency (NT) ultrasound. PSO recognized that access to nuchal translucency ultrasound during the time window when it must be performed (11 weeks and 2 days to 13 weeks and 3 days) could be limited due to availability of this service in some regions, self-isolation or quarantine, or simply because pregnant individuals wished to reduce their interactions with the medical system. Therefore, changes were made to the system to ensure that quality screening would remain accessible.

What changes were made to the screening system in response to the COVID-19 pandemic?

Effective April 2020, the following temporary changes were made:

Singleton pregnancies

Order NT if possible (as part of enhanced first trimester screening (eFTS)).
If NT is not accessible, order the second trimester maternal serum screen (MSS, now known as Second Trimester Screening or STS).
- Concurrently, MSS (STS) was optimized to match the detection rate of eFTS using a cut-off of 1 in 350 instead of 1 in 200.

Twin pregnancies

Order NT if possible.
If NT is not accessible, OHIP-funded non-invasive prenatal testing (NIPT) is available for all twin pregnancies (since there is no serum-only based MMS option).
- Furthermore, to avoid an increased burden to the resources of the specialty clinics during the pandemic, it was determined that NIPT for twin pregnancies could be ordered as a category I clinical indicator, as opposed to strictly by Maternal Fetal Medicine or Genetics specialists.

What was the impact of these changes?

The impact of these changes to the system were monitored on a continual basis with BORN data.

Singleton Pregnancies*

The MSS (STS) cut-off adjustment to 1 in 350 resulted in approximately 150 additional pregnant individuals receiving a screen positive result for trisomy 21 and therefore being eligible for funded NIPT, giving a trisomy 21 positive rate of 8.1% compared to 5.7% with the previous 1 in 200 cut-off.
The most common modality for MMS remained to be eFTS during the pandemic at 91% of the screens, just like in the year prior to the pandemic.
Therefore, while some pregnant individuals may have experienced challenges obtaining an NT ultrasound (and therefore eFTS), these data suggest minimal impact to NT ultrasound access during the pandemic.

Twin Pregnancies*

From April 2020 to December 2021, a yearly average of 501 twin gestation pregnancies received funded NIPT. This represented an additional yearly average of 253 twin pregnancies receiving funded NIPT compared to the previous fiscal year 2019-2020.

The changes to the system during this period resulted in a small increase in the number of pregnant individuals eligible for funded NIPT, with minimal impact to the overall system. Periodic analyses of registry data allowed to monitor the impact of the changes put in place throughout the pandemic. The adjustments provided a more flexible system, allowing pregnant individuals to access high-quality screening modalities when access to the health-care system was limited. Improvements to the prenatal screening system made in the context of the COVID-19 pandemic will have lasting impacts on the quality and access to prenatal screening.

What is happening moving forward?

Singleton Pregnancies*

The optimization of MSS (STS) to match the detection rate of eFTS by using a cut-off of 1 in 350 instead of 1 in 200 was set to expire 31 March 2022. With two years of performance data for MSS (STS) using a 1 in 350 cut-off now available, PSO's expert committees reviewed the data and recommended that Ontario continue with this adjusted cut-off in order to maintain an improved detection rate. Therefore, the MSS (STS) cut-off has been permanently maintained at 1 in 350, providing an expected sensitivity of 86.79%^θ and false positive rate of 7.88%^θ, compared to an 89.02% sensitivity and 6.34% false positive rate for eFTS.

Twin Pregnancies

At the end of December 2021, OHIP-funded NIPT was made available for all twin pregnancies, regardless of maternal age at estimated date of delivery or access to nuchal translucency ultrasound. This change was in response to screening performance analysis, independent of the COVID-19 adjustments discussed herein.

Data notes:

Data were extracted from the BORN Information System (BIS) on 1 Feb, 2022, using cytogenetic testing data with results reported up to June 30, 2021. 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) (01-Sep-2016 to 31-Mar-2021).
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.
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".
BORN Ontario strives to better understand how our data can be used to inform health system partners on the intersection between social determinants of health, indigeneity, and perinatal and child health outcomes. This table includes data that may or may not support reflections on indigeneity and health equity. We cannot conclusively or accurately identify the extent to which BORN data reflect indigeneity and equity-deserving groups. This pursuit is ongoing, and we appreciate your support and ideas related to enabling our efforts in pursuit of more equitable outcomes and programming.

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