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What is the nuchal translucency scan?
This ultrasound test measures a small fluid collection within the skin at the back of the baby's neck (nuchal translucency). All babies have this, but the larger the nuchal measurement the higher the chances of the baby having Down's syndrome. The nuchal test is more accurate in detecting Down's than relying on the woman's age alone. It does not tell you definitely if the baby does or does not have Down's.
What is Down's syndrome?
Down's syndrome is caused by the presence of an extra chromosome (number 21) in the cells of the developing baby. This is a result of a genetic accident occurring at the time of conception. People with Down's syndrome have severe learning difficulties, mental handicap, distinctive physical characteristics and some are prone to certain medical conditions. The degree of disability varies but there is no way of determining the severity before the baby is born.
How is my individual risk for Down's syndrome calculated?
Your individual risk for Down's syndrome will be calculated by taking into consideration:
- Your age.
- The nuchal measurement.
- The level of the hormones in your blood (ß-HCG and PAPP-A).
Is the blood test necessary?
Using nuchal translucency measurement in combination with your age we can detect 70 per cent of Down's fetuses. By adding the results from the blood the detection rate increases to 90 per cent.
Are there any other benefits of this early scan?
- It dates the pregnancy accurately.
- It diagnoses early pregnancy failure.
- It diagnoses multiple pregnancy and classifies what type.
- It diagnoses major fetal abnormalities.
Do I need a full bladder?
No. Do not drink excessively in an attempt to fill your bladder, as is the case with other types of scan.
How is the scan done?
You lie on your back whilst we scan the baby through the tummy. Very occasionally, if the pictures are not very clear, the examination may have to be performed through the vagina. Here, a very thin ultrasound probe is gently inserted into the vagina to improve the visualisation of the baby. This is not uncomfortable and again does not harm the baby.
Does the thickness of the back of the baby's neck change during pregnancy?
Yes it does. The thickness may be quite different on a week-to-week basis. For the detection of Down's syndrome the thickness must be measured between 11-14 weeks of pregnancy.
Can the thickness of the back of the neck mean anything else?
If the thickness of the back of the baby's neck is quite big other conditions may be present. These are very rare. This will be discussed further if the thickness is greater than 3mm.
What is considered 'high risk'?
A generally agreed high-risk figure is of a Down's risk of greater than 1:300. This is equivalent to 0.3 per cent chance of the baby having Down's or a 99.7 per cent chance that it doesn't.
What happens if the test shows that I am at high risk?
You will have further counselling. You will be offered an invasive test (CVS or amniocentesis). You may need to have further detailed scans and monitoring of the pregnancy.
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