Dating scan nuchal scan
If the nasal bone is visible at the scan then this will reduce the chance of your baby having Down's syndrome.
The view of the nasal bone should show three distinct lines: The first two lines, are horizontal and parallel to each other, resembling an 'equal sign'.
The crown rump length is a universally recognized term, very useful for measuring early pregnancies.
The CRL (see image above between the two white marked 1) is highly reproducible and is the single most accurate measure of gestational age.
The top line represents the skin and bottom one, represents the nasal bone.
A third line, almost in continuity with the skin, but at a higher level, represents the tip of the nose.
The 12 week scan is a routine ultrasound examination carried out at 10 to 14 weeks of gestation.
At the first trimester scan they confirm that the fetus is alive, they assess the gestational age by measuring the crown-rump length and will also look for any major problems.
In the past few years it has been seen that approximately 3 in 4 babies with Down's syndrome do not have a visible nasal bone at the time of the first trimester screening test.
During the examination, the fetus is seen by abdominal ultrasound.
Occasionally the view is not clear and it may be necessary to perform a vaginal scan.
Occasionally the nasal bone cannot be seen at 11 weeks as it is too early in the pregnancy.
If this is the case and this creates some concern then the scan can be repeated a week later.