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

Objectives: One part of the ultrasound examination of fetuses in the first trimester of gestation is visualization of the nasal bones. Numerous studies have demonstrated a correlation between the absence of nasal bones and abnormal fetal karyotype. Aim: To assess the utility of ultrasound visualization of nasal bones during the first trimester of pregnancy as a marker of the most common chromosomal trisomies. Material and methods: Ultrasound visualization of nasal bones was carried out in 941 fetuses from a high-risk group between 11 + 0 and 13 + 6 weeks of gestation. Amniocentesis was performed to determine karyotype in all 941 cases. Results:Normal fetal karyotype was observed in 847 cases,trisomy 21 in 45 cases,trisomy 18 in 16 cases and trisomy 13 in 10cases. Other abnormal karyotypes were detected in the remaining 23 cases. The absence of nasal bones demonstrated 27% sensitivity, 97% specificity and a positive predictive value of 35% as an indicator of trisomy 21 in the study group, and 12% sensitivity, 97% specificity and 12% positive predictive value for trisomies 18 and 13. Conclusions: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.