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It is this black space that you will see measured during the ultrasound scan.Currently the most accurate non invasive test for detecting Down syndrome during pregnancy is the measurement of the nuchal translucency with an ultrasound between 11 to 14 weeks of pregnancy.You do not need to have a full bladder, a moderately filled bladder is needed for a proper examination.Most parents look forward to their scan because it gives them the first glimpse of their baby.
There is no hard and fast rule for the number of scans you should have during pregnancy.
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.
First trimester ultrasonic scans may show 'soft' markers for chromosomal abnormalities, such as an increased fetal nuchal translucency (back of the neck) to enable detection of Down's syndrome fetuses.
The test is performed between 11 weeks and 13 weeks 6 days into your pregnancy.
The test cannot be performed outside this time frame as certain features that need to be seen on the scan are not present.