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.