Congenital abnormalities and their identification Flashcards
What sort of abnormalities does congenital abnormalities encompass?
Structural deformities; chromosomal abnormalities; inherited diseases; intrauterine infections and drug exposure
What is a screening test?
Available for all women and gives a measure of the risk of the fetus being affected by a particular disorder. The ‘higher-risk’ patient can then be offered a diagnostic test.
What is a diagnostic test?
Performed on ‘high risk’ women to confirm or refute the possibility.
What does a good screening test need to be?
Cheap, high sensitivity, high specificity, have an acceptable diagnostic test, condition should be serious,
What is sensitivity?
The proportion of subjects with the condition classified by the test as screen positive for the conditions
What is the negative predictive value?
The probability that a subject who is screen negative will not have the condition
What is specificity?
The proportion of subjects without the condition who are classified as screen negative
What is the screen positive rate?
The proportion of subjects who are classified as high risk by the test
What is the positive predictive value?
The probability that a subject who is screen positive will have the condition
What is the false positive rate?
The number classified as high risk who do not nevertheless have the condition
What methods can be used for prenatal testing of congenital abnormalities?
Maternal blood testing, ultrasound, fetal MRI, 3D ultrasound, amniocentesis, chorionic villus sampling, preimplantation genetic diagnosis (IVF)
What can maternal blood testing be used to prenatally test for?
Neural tube defects (Alpha fetoprotein raised), chromosomal abnormalities (beta-HCG, PAPPA, AFP, oestriol and inhibin A will be altered).
Why is AFP raised in neural tube defects?
It is a product of the fetal liver, when the fetus has an open neural tube defect maternal levels are often raised
Can US be used as a screening of diagnostic test?
Both. Screening for downs and cardiac (nuchal translucency). Diagnostic for structural abnormalities
When is amniocentesis performed?
15 weeks gestation
What is the risk of miscarriage of amniocentesis?
1%, lower risk than CVS
When is chorionic villous sampling performed?
11 weeks gestation
What is CVS used to diagnose?
Chromosomal problems, autosomal dominant and recessive conditions
What (chromosomally) is downs syndrome?
Trisomy 21
Why does trisomy 21 occur?
It is usually the result of random non-dysjunction at meiosis, although occasionally it arises as a result of a balanced chromosomal translocation in the parents
At what age of mother is Downs syndrome more common?
In older mothers (over 35)
What (chromosomally) is Edwards syndrome?
Trisomy 18
What (chromosomally) is Patau’s syndrome?
Trisomy 13
What are Edwards and Patau’s syndrome?
They are associated with major structural abnormalities and affected foetuses die in utero or shortly after birth
What is Turner’s syndrome?
Single X chromosome (X0), affected individuals are female, infertile but with normal intellect
What is Klinefelter’s syndrome?
47XXY. These males have normal intellect, small testes and are infertile
What would a US show if the fetus had down syndrome?
Thickened nuchal translucency
Some structural abnormalities
Absent or short nasal bone
Tricuspid regurgitation
What would maternal blood tests show if the fetus had down syndrome?
Low PAPPA in 1st trimester High beta-hCG (1st/2nd trimester) Low AFP (1st/2nd trimester) Low oestriol (2nd trimester) High inhibin (2nd trimester)
What prenatal tests are used to diagnose chromosomal abnormalities?
Amniocentesis and CVS
What is the ‘combined test’ used to screen for down syndrome?
US and blood test (PAPPA and beta-hCG)
What are some central nervous system structural abnormalities?
Neural tube defects, ventriculomegaly and akinesia
What are neural tube defects?
The result of failure of closure of the neural tube, neural tissue is often exposed, allowing degeneration
What is an example of a well-known neural tube defect?
Spina bifida
What can the mother take to reduce the risk of neural tube defects?
0.4mg/day folic acid
What is ventriculomegaly?
Enlargement of a ventricle(/s), particularly the lateral ventricle. Prognosis depends on the severity and cause
What medical in utero therapies are available?
Steroids to mature lungs
Antiarrhythmic drugs
NSAIDs for polyhydramnios
What examples of abdominal wall structural defects are there?
Exomphalos and gastroschisis
What is exomphalos?
Abdominal contents protrude through the anterior abdominal wall but are covered in an amniotic sac.
50% are caused by a chromosomal problem. Good prognosis after postnatal surgery
What is gastroschisis?
Congenital defect in the anterior abdominal wall just lateral to the umbilical cord
Rarely associated with other abnormalities.
>90% survive after postnatal surgery
What is a diaphragmatic hernia?
The abdominal contents herniate into the chest, causing pulmonary hypoplasia.
What is polyhydramnios?
Liquor volume increased. Normal volume varies with gestation, but deepest liquor pool >10cm generally considered abnormal
What are the causes of polyhydramnios?
Idiopathic Fetal infection Rhesus isoimmunisation Maternal disorders (DM, renal failure) Duodenal atresia Twins Fetal anomaly (Down, Edward) Fetal cardiac failure
What are the clinical features of polyhydramnios?
Maternal discomfort. Large for dates, taut uterus, fetal parts difficult to palpate
What are the complications of polyhydramnios?
Preterm labour, maternal discomfort, abnormal lie and malpresentation
How would you treat polyhydramnios?
NSAIDs to reduce fetal urine output
List 5 complications of amniocentesis.
- Preterm labour and delivery
- Chorioamnionitis
- Fetal respiratory distress
- Fetal trauma
- Red cell alloimmunisation in rhesus negative pregnancies
- Risk of miscarriage
List 5 causes of oligohydramnios.
- premature rupture of membranes
- fetal renal problems e.g. renal agenesis
- intrauterine growth restriction
- post-term gestation
- pre-eclampsia
