The impact of introducing combined first-trimester trisomy 21 screening in the French population

Background: French state health insurance has funded trisomy 21 prenatal screening for all pregnant women since decades. First-trimester combined screening was introduced nationally and funded in 2010. Objective: To evaluate the impact of the introduction, of a national policy of prenatal trisomy 21 first-trimester screening on the reduction of invasive prenatal diagnostic procedures. Methods: The results of all prenatal trisomy 21 screening and invasive diagnostic procedures were collected for the whole country over the period 2009–12. The screen-positive rates (risk cut-off 1 : 250, including isolated nuchal translucency ≥ 3.5 mm), positive predictive values and percentage of cases diagnosed prenatally were calculated. Results: Over the study period the number of women undergoing serum screening (including first- and second-trimester screening tests) increased from 678 803 to 689 651 (83 to 85% of deliveries, P < 0.0001). By 2012, first-trimester combined screening accounted for 70% of all trisomy 21 screening. The screen-positive rate decreased from 9.5 to 4.8% (P < 0.001) resulting in a 37 478 (47%) drop (P < 0.001) in the number of invasive diagnostic procedures. The positive predictive value of screening increased from 2.6 to 6.1% from 2009 to 2012 (P < 0.001), due to the higher positive predictive value of first-trimester over second-trimester screening (9.1 vs. 1.8% over the period 2010–12, P < 0.001). The percentage of prenatally diagnosed cases remained high at around 80% between 2010 and 2012. Conclusions: The policy shift from second-trimester to first-trimester trisomy 21 screening allowed to reduce the number of invasive tests. The number of antenatal trisomy 21 diagnoses increased (+2.7%) over the study period.

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