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Ultrasound screening is the most important contribution for prenatal detection of fetal developmental disorders. The time period between 11 and 14 weeks has proved to be the most suitable for detecting the majority of aneuploidies, a great number of malformations, the differentiation between mono- and dichorionic twin pregnancies and the early assessment of maternal pregnancy risks such as pre-eclampsia in order to start prophylactic treatment. The period between 18 and 22 weeks is used for the detection of structural fetal abnormalities. For this purpose a great number of clearly defined sonographic planes have to be visualized and electronically stored. The main task for the sonographer in the third trimester is to determine fetal and placental position and to detect fetal growth disorders. Using fetal Doppler studies allows determination of the optimal time and mode of delivery. In the case that a particular fetal malformation requires postnatal treatment, the mother can be transferred before birth to the most appropriate hospital. With the aforementioned sonographic techniques most of the major fetal and maternal problems can be detected on time and effective steps for a solution be taken.