Abstract
The objective of our study was to assess the visualization of nasal bone in the first trimester and its credibility, by an experienced operator in a Tertiary Fetal Medicine Center. A total of 1245 women with singleton and multiple pregnancies, who were referred for routine first trimester ultrasound at 11–14 weeks of gestation were assessed for the presence or absence of nasal bone in the fetus. The study was conducted at a Fetal Medicine Center in South India, by a highly experienced Fetal Medicine Consultant, during the period from October 2015 to December 2016. The fetal nasal bone was imaged in 1200 of these fetuses (NB +). Twenty-three patients had isolated absence of nasal bone, with no other associated markers like tricuspid regurgitation (TR), ductus venosus reversal or associated anomalies and three patients had an associated finding of TR. In 19 patients, nasal bone was imaged with difficulty. However, biochemical screening turned out to be negative in these patients and during the second trimester scan, nasal bone was present in all cases. Apart from this, five cases for which we had reported that the nasal bone was visualized normally in the 11–14 weeks scan, nasal bone was found to be absent in the second trimester scan. These patients were given the option of direct sampling. Three were found to have normal karyotype. One patient chose to terminate the pregnancy and the other patient was lost for follow up. The study points the difficulties faced by even experienced sonographers in the application of the fetal nasal bone as an additional screening tool in the first trimester scans. In order to improve the efficacy of nasal bone assessment in the prediction of trisomy 21, we recommended that the nasal bone be re-assessed during the performance of anomaly scan. The detection rate remains the same, however, the errors due to the first trimester technical difficulties can be avoided with re-assessment.
Keywords
Nasal bone - Absence of - Prenatal screening - Prenatal ultrasonography - 11–14 weeks scan - Visualization - Credibility - Nasal bone assessment
