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Biochemical screening during pregnancy - used since the early nineties in different combinations to detect fetal numerical chromosomal abnormalities (e.g. Down Syndrome) and open neural tube defects (spina bifida) - still remains controversial for a variety of reasons. Therefore a health technology assessment (HTA) was carried out to determine the medical effectiveness of the screening method. Systematic searches were performed in publication and project lists of international technology assessment institutions and in different biomedical and HTA-specific databases. The publications had to accomplish predefined criteria and were reviewed by check lists. Eighteen systematic reviews, meta-analyses and decision analyses as well as nine primary studies were used for the study. The data analyzed are highly consistent with regard to sensitivity and specificity of different combinations of biochemical and sonographical markers and stages of pregnancy. The detection rate (sensitivity) in second trimester screening averages 60% to 65% (false positive rate: 5%) when a screening covers maternal age, AFP, hCG, and uE3. Sensitivity stays the same when the screening includes Inhibin A as a fourth parameter. The detection rate in first trimester is 70% to 75% (false positive rate: 5%) on average when a combinatorial screening on maternal age, fetal nuchal translucency, PAPP-A, and free β-hCG is performed. The more common second trimester screening may cause ethical problems, because termination of pregnancy, which may be asked for by women in case of an existing fetal chromosomal abnormality, has to be performed at an advanced gestational age. Actually there are new molecular technologies which promise a significant higher screening sensitivity and will allow faster results to be obtained.