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Ultrasound imaging
Learning Outcomes
A ‘dating scan’ at 8-14 weeks to determines the stage of pregnancy and the due date
An anomaly scan at 18-20 weeks may detect serious physical problems
Dating scans are used with tests for marker chemicals which vary normally during pregnancy
Measuring a substance at the wrong time could lead to a false positive result
Suggested learning activityView ultrasound images at different stages of pregnancy.
View specialised ultrasound images - ‘marker’ nuchal translucency by ultrasound
High frequency sounds . . . .
An ultrasound scanner picks up high frequency sounds that have bounced off the foetus
A ‘dating scan’ is performed at 8-14 weeks to determine the stage of pregnancy and to calculate the due date
Dating scans are used in conjunction with biochemical tests for marker chemicals which vary normally during pregnancy
9 week foetus
scan showing features
20 week anomaly scan
Chemical markers
It is worthwhile noting that measuring a substance at the wrong time could lead to a false positive result
For example, at one stage in pregnancy the presence of a high level of a certain chemical marker may indicate that the foetus has a genetic disorder
At another stage in pregnancy the same high level would have no significance
Another scan is carried out at 18-20 weeks and this produces an ‘anomaly scan’
At this scan, checks for physical abnormalities can be made
Nuchal Translucency Scan (NT)
A NT scan helps experts to estimate, more accurately, the risk of a Down’s syndrome baby
The test is carried out at 11-14 weeks (most reliable results at this time)
It allows an assessment to be made of the thickness of fluid at the nape of the neck of the foetus
If the Nuchal Translucency exceeds a normal value then there is a risk of chromosomal abnormality (this is not a diagnostic, definite, test)
fluid exceeds ‘normal’ value
1. What is a dating scan and when is it done?
2. When is an anomaly scan done and what may it detect?
3. Which type of scan helps to estimate the risk of Down’s syndrome?
4. When is the NT scan carried out and what does it assess?
5. Is this a diagnostic test?
1. What is a dating scan and when is it done?
A ‘dating scan’ at 8-14 weeks is carried out to determine the stage of pregnancy and the due date
2. When is an anomaly scan done and what may it detect?
An anomaly scan at 18-20 weeks may detect serious physical problems
3. Which type of scan helps to estimate the risk of Down’s syndrome?
A Nuchal Translucency scan helps experts to estimate, more accurately, the risk of a Down’s syndrome baby
4. When is the NT scan carried out and what does it assess?
The test is carried out at 11-14 weeks as this gives the most reliable results at this time
It allows an assessment to be made of the thickness of fluid at the nape of the neck of the foetus
5. Is this a diagnostic test?
No
