This is normally less than 2.5mm and when seen increased (greater than 2.5mm, see image on the right) may indicate the baby has Down syndrome or may indicate another chromosomal abnormality. The nuchal translucency test will also check whether your baby has a visible nasal bone.
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.
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.
A scan maybe ordered when an abnormality is suspected on clinical grounds.
Otherwise a scan is generally booked in the first trimester to confirm pregnancy, exclude ectopic or molar pregnancies, confirm cardiac pulsation and measure the crown to rump length for dating.
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 test cannot be performed outside this time frame as certain features that need to be seen on the scan are not present.This test results in a 9095% detection rate of pregnancies that may be at an increased risk of carrying a genetical problem such as Downs Syndrome.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.You do not need to have a full bladder, a moderately filled bladder is needed for a proper examination.