Currently, 4-5% of neonates are born with congenital anomalies. One of the most important groups of these anomalies is the chromosomal aneuploidies, among which the numeric chromosomal aneuploidies have the greatest clinical role. The other important group is the structural abnormalities. The main aim of my studies was to gain a better insight into the possibilities provided by first-trimester ultrasound screening for foetal aneuploidies and other structural abnormalities. In this study, the effectiveness of first-trimester ultrasound in the screening of foetal aneuploidies was examined. Also, the association between first-trimester increased nuchal translucency thickness and foetal cardiac defects and major congenital structural malformations was studied. This book should be useful for medical professionals and future parents who are interested in early detection of fetal chromosomal and structural abnormalities.