RESUMO
A retrospective study of the different biochemical markers used in screening for Down's syndrome was carried out on serum from 18,600 women between their 15th and 18th week of pregnancy. Thirty-two sera were from women with fetal Down's syndrome. The retrospective study of these 32 sera involves: (a) the screening of the maternal serum concentrations of human chorionic gonadotropin (hCG) and of alpha-fetoprotein (AFP); (b) the evaluation of the risk of Down's syndrome when screening maternal serum concentrations of hCG alone, then the combination of the two markers and finally the maternal serum concentrations of unconjugated estriol (uE3). The mean of MOM (multiples of the median) for the pathological sera were calculated for hCG (1.91), for AFP (0.63), for the ratio hCG over AFP (3.02) and for uE3 (0.72). With the use of hCG alone we estimated a 41% detection rate for an amniocentesis rate of 5.3%, whereas when hCG was combined with AFP the detection rate approached 65% for an amniocentesis rate of 5.5% at a risk cut-off of 1:300. The results of the uE3 determination confirm the validity of this marker. The comparison of these results with other retrospective studies shows the incidence of different factors in the detection rate such as the choice of markers, the age group studied, the modes of calculating the risk and the actual cut-off chosen.
