AFP and trisomy: In order to achieve a more accuratediagnosis of trisomy 18, we must combine sonography,triple test and amniocentesis (1, 3, 5).Sensitivity of ultrasound screening for trisomy 18was reported 70% (7), while a multiple marker test[Alpha fetoprotein, human chorionic gonadotropin(HCG), Unconjucated estriol] was abnormal onlyin 43% of cases with trisomy 18 (8).