Contingent screening for Down syndrome completed in the first trimester: a multicenter study.

OBJECTIVE

To assess a new contingent screening strategy for Down syndrome completed in the first trimester.

METHODS

First-trimester screening combining nuchal translucency thickness measurement and assessment of serum analytes (combined test) was offered to pregnant women who presented for prenatal care during the first trimester to nine health centers and community hospitals in the area served by the Catalan Public Health Service. If an intermediate risk (1/101-1/1000) for Down syndrome was identified, women were referred to the Hospital Clinic Barcelona for risk reassessment that included the use of secondary ultrasound markers (nasal bone, ductus venosus blood flow and tricuspid flow). Intermediate-risk women were divided into two subgroups for further analysis: high-intermediate risk (1/101-1/250) and low-intermediate risk (1/251-1/1000). We compared feasibility and efficacy of both combined and contingent screening strategies.

RESULTS

The combined test, the first screening stage, was performed in 16 001 pregnant women, of whom 1617 (10.1%) were found to have an intermediate risk. Further division of this group showed that 1.8% (n = 289) of women were at high-intermediate risk and 8.3% (n = 1328) at low-intermediate risk. The contingent screening strategy significantly reduced the false-positive rate, from 3.0% to 1.3-1.8% (P < 0.001), without affecting the detection rate (which was 75-79% and 76%, with and without the contingent screening strategy, respectively). However, only 45% of intermediate-risk patients underwent the second screening step due to a preference among high-intermediate-risk (1/101-1/250) women for invasive testing and to low uptake among low-intermediate-risk (1/251-1/1000) women.

CONCLUSIONS

The proposed first-trimester contingent strategy reduces the screen false-positive rate without impacting on the detection rate of Down syndrome. The low compliance observed in our study may prevent its use in certain populations.