Genetics and screening for foetal abnormality Flashcards
What are the RFs for a woman having a high risk pregnancy?
- Maternal age >35y/o
- Previous abnormal baby
- FHx of inherited condition
What is also looked for in the gestational scan?
- Viability
- Gestational age
- Chorionicity
- FNT
- Malformation
What is FNT a measure of?
Fluid accumulation in the neck
What is the PPV of FNT?
Only 4% - therefore 96% who undergo FNT actually don’t have a chromosomal abnormality
What is AFP?
Alpha-fetoprotein
Where is AFP produced?
Foetal liver and GI tract
What may high levels of AFP indicate?
- Open neural tube defect
- Exomphalos
- Posterior urethral valves
- Nephrosis
- GI obstruction
- Teratoma
- Turner’s syndrome
What are the elements of the combined test for screening for Down’s syndrome?
FNP + PAPP-A + beta-hCG
Why may FNP not be able to be measured?
- Maternal obesity
2. Foetus lie
What should be offered if FNP can’t be measured?
The triple or quadruple test
What are the elements of the triple test?
AFP + estriol + beta-hCG
What are the elements of the quadruple test?
AFP + estriol + beta-hCG + inhibin A
Following the anomaly scan - what should prompt a referral to a foetal medicine specialist?
- Nuchal fold >/=6mm
2. >=2 soft markers - 1) increased nuchal thickness; 2) choroid plexus cysts; 3) echogenic bowel
What is CVS?
A placental biopsy
When should CVS be performed?
Not before 10 weeks, and not after 20 weeks
What is the foetal loss rate?
4/100
What are the problems with CVS?
- Does not detect NTDs
2. May cause foetal malformation
When should amniocentesis be performed and why?
After 15 weeks, because before then there is an increased rate of foetal loss, an increased incidence of foetal talipes and respiratory morbidity
What is the foetal loss rate in amniocentesis?
1/100 at 16 weeks
What defines recurrent spontaneous miscarriage (RSM)?
> /=3 miscarriages that occur in succession
What is a late miscarriage?
14-24 weeks
When is it defined as a stillbirth?
> 24 weeks
What are the possible causes of RSM?
- Chromosomal translocation
- Anti-phospholipid syndrome
- Infection - BV can cause late RSM
- Thromophilia
- Endocrine - e.g. PCOS
- Anatomical abnormality - e.g. cervical incompetence or uterine abnormality
What are the 3 main types of abnormal morphogenesis?
- Deformation
- Malformation
- Disruption
What are malformations caused by?
An intrinsic problems within the developing structure
What is a deformation caused by?
An extrinsic force on a normally developing or developed structure - usually occur late in foetal life caused by a lack of foetal movement through one of either 1) mechanical factors; 2) malformation factors; 3) functional factors
What is a disruption caused by?
A destructive force acting upon an otherwise normal developing structure
What is the VATER association?
V - vertebral anomalies A - anal atresia T - tracheo- E - esophageal fistula R - radial and renal anomalies
