First trimester contingent testing with either nuchal translucency or cell-free DNA. Cost efficiency and the role of ultrasound dating.

OBJECTIVE To evaluate the performance and cost efficacy of different first-trimester contingent screening strategies based on an initial analysis of biochemical markers. DESIGN Retrospective study. SETTING Swedish National Quality Register for prenatal diagnosis. POPULATION 35,780 women with singleton pregnancies. METHODS Serum values from first trimester biochemistry were re-analyzed in a contingent approach. For risks between 1:40 and 1:1000, risk estimates from nuchal translucency measurements were added and outcomes were compared using either a final cut-off risk of 1:200 to proceed with invasive testing or offering non-invasive prenatal testing. In a subgroup of 12,836 women with regular menstrual cycles the same analyses were performed using data on the last menstrual period for determining gestational age. The costs of detecting one case of aneuploidy were compared. MAIN OUTCOME MEASURES Comparison of screening strategies. RESULTS The detection rate was the same (87%) in the contingent group as in complete combined screening, with only 41% requiring a nuchal translucency scan. As an alternative, offering non-invasive prenatal testing to the intermediate risk group would result in a detection rate of 98%, but the cost to detect one case of trisomy 21 would be 83% higher than the cost associated with traditional combined screening. CONCLUSIONS First trimester examination using a contingent approach will achieve similar results compared with full combined screening. Non-invasive prenatal testing will not be cost-effective when a high proportion of pregnancies need further testing.