In this prospective study, we recorded details on 3,685 fetuses with congenital structural abnormalities from an unselected population of women who underwent routine ultrasound examinations during their pregnancies. Overall, 2,262 fetuses were diagnosed as being abnormal before birth (sensitivity = 61.4%). The total number of abnormalities was 4,615, of which 1,733 (37.5%) were major abnormalities. The overall number of detected abnormalities was 2,593 (sensitivity = 56.2%). If only major abnormalities were considered, the sensitivity rose to 73.7%, compared to only 45.7% for the minor abnormalities. Within each severity group, the accuracy of detection varied across systems. For the major abnormalities, it was higher for the central nervous system (88.3%) and urinary tract (84.8%), but lower for heart and great vessels (38.8%). Detection of minor abnormalities was also effective for the urinary tract (89.1%), but not for the heart and great vessels (20.8%) and the musculoskeletal system (18%).