Abstract
Objective To assess the reliability of nasal bone (NB) as an aneuploidy marker in the first
trimester vs. second trimester and to highlight the technical difficulties in evaluating the nasal
bone at 11–14 week scan.
Methods Nasal bone was examined in 4478 women who enrolled for nuchal translucency (NT) scan
and NB was assessed in both midsagittal and coronal planes. Risk assessment was done
based on serum biochemistry and NT without including the NB status. Absence of NB
was confirmed at 17 week and aneuploidy risk was modified from the obtained first
trimester risk. The midsagittal images from the cases with absent NB were randomly
assorted among 81 normal ones and were peer reviewed.
Results Nineteen fetuses had absent NB in the first trimester, of which five had NT above
the 90th percentile. In the remaining 14 cases followed up at second trimester, nasal
bone was present in 3 cases in the subsequent scan. Five of 11 cases were screen positive
after modifying the risk and were counseled appropriately. In retrospective evaluation
of the 100 images, concordance was obtained only in 76%, reflecting the observer variability.
Down’s syndrome was confirmed in 4 cases of which three also had an increased NT.
Conclusions Routine inclusion of NB in first trimester risk assessment with conventional midsagittal
view alone in all cases may lead to an increased number of false positives. Inclusion
in the second trimester would still have the same detection rate but would eliminate
technical difficulties of imaging NB in the first trimester.
Keywords
Nasal bone - Aneuploidy - Retronasal triangle - Midsagittal plane - Equal sign - First
trimester screening - Nuchal translucency - Non-invasive prenatal testing
