Which of the following ultrasound marker is associated with greatly increased risk for Trisomy 21 in fetus?

Among the ultrasound findings given in the question, increased nuchal thickness is associated with greatest increased risk for Trisomy 21 in fetus. Nuchal translucency thickness >3mm is associated with an increased risk of chromosomal anomaly. Serum assays combined with maternal age and nuchal translucency, helps in the diagnosis of downs syndrome in 87% cases. In 95% cases of downs syndrome, there are three copies of chromosome 21, which occur due to non dysjunction of chromosomes. Remaining cases are either mosaics or those which occur due to trans-location of chromosomes. Ref: Textbook of Obstetrics By Padubidri and Anand, Page 467; Nine Healthy Months: All You Need to Know By Charles Hux M D, Page 79; Ultrasound in Obstetrics and Gynecology, Volume 1 By Eberhard Merz, 2nd Edition, Page 45