The nasal bone is oftern small or absent in people with Downs syndrome.
In view of this we examine fetus at the time of the nuchal scan to see
if the bone is present or absent.
In the majority of cases the bone is absent in Downs syndrome. However,
this is not usually an isolated feature and oftern there are other
problems or concerns raised with the scan or the blood test.
If we cannot see the nasal bone at your visit and you are less than 12
weeks pregnant then we sometimes bring you back for a repeat scan as
often the bone then grows during that period of 1 to 2 weeks. This would
be discussed with you at the time of the scan.
It is more common to find an absent nasal bone in oriental fetuses than
caucasion fetuses but the rate of Downs syndrome is still the same. So
the effect of cultural background has also got to be taken into account
for this examination.
In caucasians the bone is absent in the normal population in 1 to 2% of
cases
