During the first trimester of pregnancy, the combination test is used for an assessment of the individual risk of Down's syndrome. Several factors have an effect on the variance of the risk estimates. In this context, special attention is given to the interpretation of test results based on centre-specific medians for gestation and those based on published normal medians that are derived from large databases that have a proven track record in terms of detection rates. Centre-specific medians could be used, provided test performance is closely monitored and stays within acceptable limits. In order to reduce undue anxiety from conflicting false-positive test results, all components that yield the risk estimates should be standardised. To achieve this goal, the government should no longer delay the implementation of a national, first trimester, prenatal screening programme for Down's syndrome as was recommended by the Health Council of The Netherlands. Such a programme should incorporate strict guidelines for information, risk communication, quality assurance and feedback.