[Evaluation of a programme for the prenatal screening for Down's syndrome by ultrasonographic nuchal translucency measurement and serum determinations in the first trimester of pregnancy]

Abstract

Objective: To determine the diagnostic value of the combination screening test for Down's syndrome in women in the first trimester of pregnancy.

Design: Secondary data analysis.

Method: The data from 2026 consecutive combination tests that were carried out in the period 1 May 2001-31 October 2003 in the VU Medical Centre in Amsterdam, The Netherlands, were analysed. The combination test comprised ultrasonographic neck fold measurement together with determination of the serum levels of free human beta-chorionic gonadotrophin and pregnancy-associated plasma protein A. The chance of Down's syndrome in the foetus was calculated using the median values of the Fetal Medicine Foundation (FMF) and medians based on the population in the VU Medical Centre. A chance > or = 1:200 was considered elevated. Follow-up data were collected from the medical records and from patient reports.

Results: The data from 25 patients were excluded because of incompleteness of the investigation or the presence of diabetes mellitus in the pregnant subject. Follow-up data were obtained from 1759 of the 2001 remaining women (88%). Of the 1759 women, 49% were < or = 35 years old and 51% were > or = 36 years of age. Down's syndrome was diagnosed in 21 pregnancies, 16 of which were in the advanced maternal age group of patients. The detection percentage of Down's syndrome by nuchal translucency measurement was 67 with 3 false-positives when calculated on the basis of the FMF-medians and 76 with 6 false-positives when calculated on the basis of the VU Medical Centre medians. With the combination test, the detection percentage of Down's syndrome was 86 with 11 false-positives when calculated on the basis of the FMF-medians and 90 with 5 false-positives when calculated on the basis of the VU Medical Centre medians.

Conclusion: The diagnostic value of the first-trimester combination test was greater than that of only nuchal translucency measurement. Moreover, the diagnostic value was greater if the chances were calculated on the basis of the median values of the VU Medial Centre population than when other median values were used.