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Keywords:

  • nuchal translucency;
  • Down syndrome;
  • biochemical markers;
  • first-trimester screening;
  • Combined Test

Abstract

Objective

To assess the effectiveness of the Combined Test in the prenatal detection of trisomy 21 in the general pregnant population using a new timing for the screening approach.

Methods

First-trimester maternal serum biochemical markers (pregnancy-associated plasma protein-A and free-β hCG) were determined in maternal serum at 7 to 12 weeks. Fetal nuchal translucency and gestational age were assessed at the 10- to 14-week ultrasound scan. A combined risk was estimated and delivered to the women the same day. When the risk was 1:250 or above, chorionic villus sampling was offered.

Results

Mean gestational age at biochemistry was 9.4 weeks, being 12.3 at ultrasound. In the 2780 studied pregnancies with a complete follow-up, observed detection rates were 88% (7/8) for trisomy 21 and 75% (3/4) for trisomy 18, with a 3.3% (92/2765) false-positive rate.

Conclusion

The Combined Test, assessing biochemistry and ultrasound at individually optimal ages in the first trimester, showed an 88% detection rate for trisomy 21 with a remarkably reduced false-positive rate (3.3%). Copyright © 2004 John Wiley & Sons, Ltd.