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First-trimester combined test screening for Down syndrome 2006-2008

Downsyndroom-kansbepaling met de eerstetrimestercombinatietest 2006-2008

Synopsis

Between 2006 and 2008, the use of the first trimester combined test in pregnant women reliably predicted 70 % of all Down's syndrome pregnancies in the Netherlands, a slight decrease as compared to the performance of 2004-2006. The number of test requests increased slightly during 2006-2008 and the maternal age at the time of testing was slightly lower compared to the previous period. The RIVM received reports on the outcome of the pregnancy from 63 % of the total number of tests performed, but after partial recall. These results are documented in this third evaluation of the first trimester combined test. The evaluation was performed on the instructions of the Centre for Population Research (RIVM), ordered by the Ministry of Health, Welfare and Sports (VWS). The first trimester combined test is a risk estimation test using the nuchal translucency (NT) measurement and the serum concentrations of two biochemical markers in maternal blood. The NT measurement is the sonographic measurement of a fluid deposit in the neck of the fetus. The serum markers are pregnancy-associated plasma protein-A and the free ß subunit of human chorion gonadotropin (fBeta-hCG). The value of these parameters and the maternal age are then combined to calculate the risk of the unborn child having Down's syndrome. In the current report, the risk estimation has been combined with the outcome of the pregnancy and represents an analysis of 19,172 serum tests for which both risk and outcome are available. Whilst this report focuses on the results of the RIVM screening laboratory, it also presents data from other regional laboratories. The results from the various laboratories are comparable. Finally, recommendations for improving the screening test have been proposed. Here, we propagate to use the fetal crown-rump length measured at the moment of the nuchal translucency-measurement to calculate the gestational age at blood sampling. The continued efforts of the RIVM to further enhance the test performance will include the implementation of this practice.
 

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