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Objective Antenatal reflex DNA screening for Down’s syndrome has a high screening performance. We aimed to determine the performance of trisomy 18 and trisomy 13 reflex DNA screening when added to Down’s syndrome screening. Methods In our modelled screening protocol, women provide two samples: a serum sample for a Combined test and a plasma sample for a possible DNA test. Women with Down’s syndrome, trisomy 18, or trisomy 13 Combined test risks above a single cut-off have a reflex DNA test using the plasma sample, without the need to recall them to collect another sample and provide counselling. Women with a failed DNA test (after a second attempt using a fresh plasma sample) have an Integrated test, and are classified as positive if any of the Down’s syndrome, trisomy 18, or trisomy 13 Integrated test risks are greater than 1 in 25. Results At 1 in 800 term risk cut-offs for Down’s syndrome, trisomy 18, and trisomy 13, an estimated 10% of women are reflexed to DNA screening, yielding a 91% Down’s syndrome detection rate, an 89% trisomy 18 detection rate, and a 79% trisomy 13 detection rate for a 0.05% false-positive rate. At a 1 in 1900 term risk cut-off for Down’s syndrome, trisomy 18, or trisomy 13, an estimated 20% of women are reflexed to DNA screening, and this yields a 94% Down’s syndrome detection rate, a 92% trisomy 18 detection rate, and an 84% trisomy 13 detection rate for a 0.10% false-positive rate. Conclusion Reflex DNA screening for trisomies 18 and 13 can be usefully added to reflex DNA screening for Down’s syndrome. [ABSTRACT FROM AUTHOR]

Objective To estimate the performance of antenatal sequential Integrated screening for Down’s syndrome (DS), trisomy 18 (T18) and trisomy 13 (T13), in which women have first trimester testing for each disorder; those above specified risk cut-offs are screen-positive, and the remainder continue to Integrated testing, using first and second trimester screening markers together. Methods Published screening marker parameters and Monte Carlo simulation were used to calculate detection rates (DR’s) and risk cut-off levels for specified false-positive rates (FPR’s), and DR’s and FPR’s for specified risk cut-offs. We compared this screening performance with that based on all women having Integrated tests. Results Sequential Integrated DS screening detects 71% of DS pregnancies at the first trimester stage at a 0.5% FPR. For an overall 2% FPR, the DS DR is 92%, the same screening performance as the Integrated test performed on all women. Sequential Integrated T18 and T13 screening detects 70% of T18 and 53% of T13 pregnancies at the first trimester stage at a 0.05% FPR for each. The overall T18 and T13 DR’s are 96% and 72% respectively at 0.2% FPR, the same screening performance as with Integrated tests performed on all women. Increasing the overall FPR’s does not materially increase the DR’s for any of the three disorders. Conclusion The performance of sequential Integrated screening is similar to the performance if all women have an Integrated test, but has the advantage of identifying most DS, T18, and T13 pregnancies a few weeks earlier. [ABSTRACT FROM AUTHOR]

Objective: To compare the performance of antenatal screening for Down's syndrome (DS), trisomy 18 (T18), and trisomy 13 (T13) using a single risk of being affected by one of the three disorders, with the performance using separate risks for each disorder. Methods: Screening performance was estimated using Monte Carlo simulation based on published parameters for the Integrated, Combined, and Quadruple tests. Detection rates (DRs) were calculated using a single risk and separate risks for each disorder at given false-positive rates (FPRs). Results: With separate risks, using a 3% DS test FPR and 0.2% FPRs for the T18 and T13 tests, the overall FPRs for the Integrated and Combined tests are both 3.3%. For the same overall FPR (3.3%), the use of a single risk with the Integrated test increases the T13 DR from 76% to 82%, with unchanged DS and T18 DRs (94% and 92% respectively). With the Combined test, it increases the T13 and T18 DRs (from 89% to 91% and 77% to 81% respectively), with unchanged DS DR (85%). With separate risks, using a 5% DS test FPR and 0.2% FPRs for the T18 and T13 tests, the overall FPR for the Quadruple test is 5.4%. For the same overall FPR (5.4%), the use of a single risk increases the T18 DR from 61% to 67% with unchanged DS and T13 DRs (87% and 33% respectively). Conclusions: Reporting a single risk estimate for the three disorders is less confusing than reporting separate risks and can yield the same or better screening performance. [ABSTRACT FROM AUTHOR]

The article described a study that evaluated the impact of screening for Down's syndrome on the prevalence of live births and antenatal diagnoses of Edwards and Patau syndrome. As mentioned, the study concluded that around 700 women per year had a pregnancy with Edwards or Patau syndrome, with over 90% of these pregnancies were detected antenatally, with the increased use of first trimester screening for Down's syndrome resulting in the reduction in the mean gestational age at diagnosis.