Down's Syndrome Flashcards
What are the percentage breakdown of causes of trisomy 21?
- 95% due to non-dysjunction (85% maternal, 15% paternal)
- 4% due to translocation (usually Robertsonian)
- 1% mosaicism
Why do we need to specifically consider the needs of children with Down syndrome?
- Congenital abnormalities more common
- Acquired medical problems more likely
- LD may make it less likely for them to complain of symptoms
- Some symptoms assumed to be ‘part of syndrome’ and left untreated
40-50% of children with Down syndrome suffer from congenital heart disease. What types can manifest?
- Atrioventricular septal defect
- Ventricular septal defect
- Valve defects
- Patent ductus arteriosus
- Tetralogy of fallot
What serum markers were postulated for Down syndrome screening?
- Alpha-fetoprotein (AFP)
- Human chorionic gonadotrophin (HCG)
- Unconjugated estriol (ES3)
- Inhibin A
- Pregnancy associated plasma protein A (PAPPA)
- Newer markers (ADAM12)
What is ‘multiple of the median’ in the context of Down syndrome screening?
The serum marker conc for a pregnant woman divided by the median conc value for unaffected pregnancies of the same gestational age
Give an example of how Multiple of the median is calculated?
- If measured value is 30 and median AFP for this gestational age is 30 then for this pregnancy = 1.0 MoM
- If measured value is 75 and median AFP for this gestational age is 30 then for this pregnancy = 2.5 MoM
How do AFP values differ between trisomy 21 affected and unaffected pregnancies?
Values are lower in affected pregnancies
MoM principles can also be applied to ultrasound measurements. What measurement is generally used?
Nuchal translucency (NT) - on average this is larger in affected
What is the main thing that can affect the prior odds for Bayes in context of Down syndrome screening?
Previous Down’s pregnancy
A multitude of different testing strategies can be used for Down syndrome screening - which are the best?
Those using serum AND ultrasound markers e.g.:
- Combined test: PAPPA, fbHCG and NT (11 wks 1 day to 14 wks 1 day)
- Quadruple test: AFP, HCG, uE3, inhibin-A (15 wks 0 days to 20 wks 0 days)
Why is the natural incidence of Down syndrome increasing?
- age of child bearing is increasing
- birth incidence static in UK despite screening and majority of affected foetuses being terminated
- Life expectancy of people with Down syndrome increasing rapidly
- Challenge to health and social care to meet needs of an increasingly older population of people with Down syndrome
What are some of the justifications for Down syndrome screening?
- significant LD
- susceptible to whole range of medical problems
- need support through life
- less likely to make economic contribution to society
- considerable additional cost to society for education, health and social care
What are some of the uptake stats for Down syndrome screening?
- Majority of women opt into screening
- 90% with a Confirmed antenatal diagnosis elect to terminate
- Screening/early diagnosis allow termination early in pregnancy
What are some of the issues relating to the screening itself?
- public and professional understanding of what risk screening means
- false positives can lead to invasive tests and loss of unaffected foetus as well as parental anxiety
- false negatives reassure women who may otherwise have considered invasive testing and influences adjustment in women who do have an affected baby
Does antenatal screening help if you are not considering termination?
- Gives time to adjust to new situation
- Opportunity to find out information about Down syndrome
- prompts additional scanning for anomalies more common in Down syndrome
- may influence time, place and mode of delivery
