The aim of this study was to present our preliminary data about nasal bone measurements at 11 - 14 weeks of pregnancy. This study was conducted in our prenatal unit between 2000 and 2003. A total of 642 pregnant women ( single pregnancies) were enrolled into the study. During the first trimester of pregnancy, crown-rump length, nuchal translucency thickness, and fetal nasal bone length measurements and ductus venosus Doppler images were evaluated. The distribution of absent or small nasal bones in both normal fetuses and in those having some pathological conditions was compared by statistical analysis. p < 0.05 was considered significant. Nasal bone evaluation was successful in 600 of 642 (93.4%) ultrasound examinations. The linear regression line showed a significant positive slope with increasing crown-rump length ( r = 0.54, p < 0.001). Absent or small nasal bones were more common in abnormal than in normal fetuses ( p = 0.007). It is clear that the fetal nasal bone is becoming a powerful tool in prenatal screening for aneuploidy. Larger studies to be performed in a low-risk population are needed to assess whether the measurement of the nasal bone length provides additional benefits beyond the assessment of the presence or absence of the nasal bone. Copyright (C) 2004 S. Karger AG, Basel.