| Abstract: | The different strategies applied for Down syndrome (DS) screening in a single center are presented and the results are analyzed taking into account the number of invasive procedures needed for the diagnosis of one affected pregnancy. The use of advanced maternal age as a single criterion, from 1980 to 1992 proved to be poorly effective since 102 amniocentesis are needed to diagnose one DS affected pregnancy (1:102) or 52 to diagnose any aneuploidy (1:52) With the use of second trimester screening with serum markers (AFP and hCG) at 14-18 weeks in 8711 women less than 38 years, from 1993 to 1999 the ratios were improved to 1:82 and 1:47 respectively. With the introduction of the combined test in 1999 using free hCG, PAPP-A (sampling at 9-10 weeks) and NT (measured at 12 weeks) in 3644 women under 38 years, and gestational weeks adjusted by US in 3644 singleton pregnancies with complete follow-up, the ratios were substantially improved to 1:16 procedures for DS or 1:8 for any aneuploidy. The detection rate achieved was 90% for a false positive rate of 3.4%. Comparing the different strategies applied in our Unit it is clear that the combined test applied in the first trimester provides a substantial improvement in detection rates and reduction of unnecessary invasive testing. |
