Prenatal Diagnosis Unit, Institute of Gynecology, Obstetrics and Neonatology, Hospital Clinic, University of Barcelona Medical School, Barcelona, Catalonia, Spain. aborrell@medicina.ub.es
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-beta 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 and Sons, Ltd.