Antenatal ultrasound screening for birth defects is increasingly becoming a routine procedure of prenatal care. Prenatal detection of malformations and subsequent adjustment of obstetric management are essential for secondary prevention. It is unknown whether ultrasound screening is effective in all pregnant women, or should only be performed in high risk populations. From 1990-1994, 20,248 livebirths, stillbirths and abortions underwent physical and sonographic examinations and anamnestic data were collected. To identify the high risk group, case control analyses of births with one of the 23 selected major malformations (controls) were performed with respect to anamnestic risk factors. All women had at least three routine ultrasound scans. The selected malformations were diagnosed in 298 children; 95 (30.3 per cent) were diagnosed antenatally. Detection rates were: CNS (68.6 per cent), gastro-intestinal tract (42.3 per cent), urinary system (24.1) per cent), heart (5.9 per cent). Complications during pregnancy were calculated as indicators of congenital anomalies: premature labour (< 28 week) OR 4.7 (3.8-5.9), placental insufficiency OR 1.9 (1.1-2.7) and vaginal bleeding OR 1.5 (1.2-1.8), etc. Antenatal routine ultrasound screening is not effective risk populations. Anamnestic risk factors risk factors during pregnancy may be essential indicators for identifying high risk populations. We propose screening of the described high risk pregnancies (about 22 per cent of all pregnancies) to be performed by specially trained and highly experienced ultrasonographers to increase sensitivity rates and benefit cost effectiveness.