The absence of fetal nasal bones in ultrasound examination between 11 + 0 and 13 + 6 weeks of gestation versus the occurrence of trisomies 21, 18, and 13.

The absence of nasal bones in ultrasound examination in the first trimester of pregnancy is characterized by low sensitivity and high specificity as a marker of the most common trisomies. Visualization of fetal nasal bone is a poor marker of aneuploidy and should not be taken into account in risk calculation algorithms.