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Introduction. The evaluation of fetal long bone measurements, particularly femur length, is essential in assessing fetal biometry, gestational age, size, growth, and in identifying various abnormalities. This study explores the diagnostic value of long bones length in detecting conditions such as Down syndrome and skeletal dysplasia. A femur length below the 10th percentile for gestational age is consistently associated with Down syndrome, while an extremely short femur length often indicates skeletal dysplasia. Humeral length, particularly when small compared to the biparietal diameter, serves as an additional marker for Down syndrome risk. The accurate diagnosis requires measuring all long bone segments, while the femur/abdominal circumference ratio serves as a discriminator for lethal skeletal dysplasia. Complete fetal anatomic evaluation is crucial in the presence of a short femur. This poster presents the current state of the art in the ultrasonography of fetal long bone evaluation. Materials and method. The present paper was realized by synthesizing the data published in the last 30 years regarding fetal long bones ultrasound assessment found on Google Scholar and PubMed, using for filtering the keywords: “femur length”, “humerus length”, “ultrasound”, “trisomy”, and “skeletal dysplasia”. Results. Femur length is a standard parameter measured during fetal biometry assessment. A shortened femur for gestational age may raise the suspicion for fetal growth restriction, trisomy 21 or skeletal dysplasia. In certain cases, it may be the first hint for aneuploidies or skeletal dysplasia. Femur and humerus length can be used to adjust the risk for trisomy 21. When facing a shortened femur, a complete survey of all fetal long bones is mandatory, as it may unveil a potentially severe skeletal anomaly. Conclusions. Ultrasound measurement of fetal long bones and the ratio between different skeletal measurements can be the key for the prenatal diagnosis of fetal skeletal dysplasia or can rise the suspicion of a fetal aneuploidy that can determine further investigations for establishing or excluding such a condition of the fetus. [ABSTRACT FROM AUTHOR]