[Unusual behavior of serum markers in risk evaluation for trisomy 21].

Screening of Down syndrome using serum markers is based on statistic risk determination calculated from the results of markers. An increased risk of fetal Down syndrome is associated with high hCG levels and low AFP levels in maternal serum. In the daily practice, the use of these two markers also leads to observation of different analytical patterns. We reviewed these patterns according to published data and our own experience. Some patterns are well documented (neural tube defects or trisomy 18) some of them remain unexplored. Numerous difficulties are encountered in the clinical use of these markers patterns: lack of consensus for their analytical definition, problems in interpretation, lack of regular dispositions.