Population screening for fetal trisomy 21: easy access to screening should be balanced against a uniform ultrasound protocol

Objectives To evaluate the performance of a first‐trimester fetal aneuploidy screening program, with a documented underestimation of nuchal translucency thickness measurements (NT) compared to the Fetal Medicine Foundation (FMF) reference range. Methods We analysed the data of Algemeen Medisch Laboratorium (AML) in Antwerp, Belgium, on combined screening with pregnancy‐associated plasma protein‐A (PAPP‐A), free β‐human chorionic gonadotropin (FB‐hCG) and NT. NT‐multiples of the median (MoM), relative to the FMF reference range, were used for risk calculations. Results The proportion of first‐trimester screening tests in the total of serum screening tests increased from 1.3% (125/9424) in 2000 to 53.1% (6577/12 377) in 2003. Only 11.4% (1514/13 267) of NT measurements were performed according to FMF criteria. The 80.8% (21/26) trisomy 21 (T21) detection rate (DR) at cut off 1:300 resulted from maternal serum screening. NT measurements did not add to this DR, but reduced the false‐positive rate from 16.8% (2212/13181) to 8.6% (1130/13181). Only 23.8% (5/21) of T21 detections were by FMF trainees. Conclusion Easy access to screening and maternal serum parameters accounted for the majority of T21 detections in our first‐trimester combined screening program. Copyright © 2005 John Wiley & Sons, Ltd.