[Second trimester sonographic screening for Down's syndrome and other chromosomal abnormalities].

Aim: To assess the effectiveness of second trimester sonographic screening for Down syndrome [DS] and other chromosomal abnormalities [ChrA].

Materials And Methods: In 1157 singleton pregnancies (15-21 weeks of gestation), including 18 with ChrA (13-DS, 5-other) an expert level detailed sonographic study was performed. The following parameters were analyzed: incidence and type of abnormal sonographic findings in chromosomally normal and abnormal fetuses, sonographic screening sensitivity and specificity (for DS and for other ChrA), positive predictive value [PPV] for DS of the most frequent sonographic markers, negative predictive value [NPV] of the normal genetic sonogram.