With an incidence of 1 in 700, Down syndrome (Trisomy 21) is the most common autosomal abnormality among live births. The risk increases with the mother's age. A reliable screening result is of great importance. The measurement of nuchal translucency has established itself as the most important ultrasound marker in first trimester screening since its introduction by Nicolaides and colleagues in the early 1990s. Approximately 80% of Down syndrome fetuses are detected when maternal age is combined with a measurement of nuchal translucency between gestational weeks 11+0 and 13+6. How learnable is the measurement of nuchal translucency? And is there a difference in performance between already certified examiners and those who are still inexperienced? The author, Mercedes Juliana Art, provides introductory information on first trimester screening and the various forms of trisomy. The book then addresses these questions through the analysis of a prospectively conducted study. It is aimed at medical students, doctors, and biomedical technical analysts.