THE RELEVANCE OF THE GESTATIONAL-AGE WITH REGARD TO THE INDIVIDUAL RISK CALCULATION FOR FETAL DOWN-SYNDROME IN THE COURSE OF SERUM SCREENING

Purpose: Individual risk assessment for fetal Down syndrome by use of serum markers (known as triple screening) involves several systematica l errors which may significantly reduce the specificity of risk calcul ation. Concentrations of serum markers as human choriongonadotropin (h CG), unconjugated estriol (uE(3)), and alpha-fetoprotein (AFP) are sig nificantly correlated with the gestational age. Is it possible to mini mise misjudgement of the gestational age as one of the most common and important sources of error in risk calculation? Method and Materials: The present study includes 11207 cases of routine triple-screen exami nations where gynaecologists reported in combination: the individual d ata of crown-rump length (CRL) - 1 st trimester, biparietal diameter ( BPD) - 1 st/2nd trimester, and gestational age derived from the doctor 's specific biometrical criteria and tables. All these data were conve rted to gestational days using standardised tables and were extrapolat ed to the day of blood sampling. The resulting distributions of differ ences in gestational age estimation were compared to each other. Resul ts: Comparisons revealed that the gestational age reported by the gyna ecologists was overestimated in 73.4% of cases as to the age derived f rom BPD, and in 63.2% of cases as to the age derived from CRL. Compari ng the gestational age derived from CRL (Ist trimester) and BPD (2nd t rimester) only 55% of cases were overestimated and 34.7% of cases were underestimated by BPD. Conclusion: The systematical increase of calcu lated risk caused by overestimation of the gestational age results in a surplus of indicated amniocenteses which may by avoided by the use o f specific sonographical parameters (CRL - 1st trimester, BPD - 2nd tr imester) and by the use of standardised tables.