Congenital abnormalities and their identification

Question 1

What sort of abnormalities does congenital abnormalities encompass?

Answer 1

Structural deformities; chromosomal abnormalities; inherited diseases; intrauterine infections and drug exposure

Question 2

What is a screening test?

Answer 2

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.

Question 3

What is a diagnostic test?

Answer 3

Performed on ‘high risk’ women to confirm or refute the possibility.

Question 4

What does a good screening test need to be?

Answer 4

Cheap, high sensitivity, high specificity, have an acceptable diagnostic test, condition should be serious,

Question 5

What is sensitivity?

Answer 5

The proportion of subjects with the condition classified by the test as screen positive for the conditions

Question 6

What is the negative predictive value?

Answer 6

The probability that a subject who is screen negative will not have the condition

Question 7

What is specificity?

Answer 7

The proportion of subjects without the condition who are classified as screen negative

Question 8

What is the screen positive rate?

Answer 8

The proportion of subjects who are classified as high risk by the test

Question 9

What is the positive predictive value?

Answer 9

The probability that a subject who is screen positive will have the condition

Question 10

What is the false positive rate?

Answer 10

The number classified as high risk who do not nevertheless have the condition

Question 11

What methods can be used for prenatal testing of congenital abnormalities?

Answer 11

Maternal blood testing, ultrasound, fetal MRI, 3D ultrasound, amniocentesis, chorionic villus sampling, preimplantation genetic diagnosis (IVF)

Question 12

What can maternal blood testing be used to prenatally test for?

Answer 12

Neural tube defects (Alpha fetoprotein raised), chromosomal abnormalities (beta-HCG, PAPPA, AFP, oestriol and inhibin A will be altered).

Question 13

Why is AFP raised in neural tube defects?

Answer 13

It is a product of the fetal liver, when the fetus has an open neural tube defect maternal levels are often raised

Question 14

Can US be used as a screening of diagnostic test?

Answer 14

Both. Screening for downs and cardiac (nuchal translucency). Diagnostic for structural abnormalities

Question 15

When is amniocentesis performed?

Answer 15

15 weeks gestation

Question 16

What is the risk of miscarriage of amniocentesis?

Answer 16

1%, lower risk than CVS

Question 17

When is chorionic villous sampling performed?

Answer 17

11 weeks gestation

Question 18

What is CVS used to diagnose?

Answer 18

Chromosomal problems, autosomal dominant and recessive conditions

Question 19

What (chromosomally) is downs syndrome?

Answer 19

Trisomy 21

Question 20

Why does trisomy 21 occur?

Answer 20

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

Question 21

At what age of mother is Downs syndrome more common?

Answer 21

In older mothers (over 35)

Question 22

What (chromosomally) is Edwards syndrome?

Answer 22

Trisomy 18

Question 23

What (chromosomally) is Patau’s syndrome?

Answer 23

Trisomy 13

Question 24

What are Edwards and Patau’s syndrome?

Answer 24

They are associated with major structural abnormalities and affected foetuses die in utero or shortly after birth

Question 25

What is Turner's syndrome?

Answer 25

Single X chromosome (X0), affected individuals are female, infertile but with normal intellect

Question 26

What is Klinefelter's syndrome?

Answer 26

47XXY. These males have normal intellect, small testes and are infertile

Question 27

What would a US show if the fetus had down syndrome?

Answer 27

Thickened nuchal translucency Some structural abnormalities Absent or short nasal bone Tricuspid regurgitation

Question 28

What would maternal blood tests show if the fetus had down syndrome?

Answer 28

``` Low PAPPA in 1st trimester High beta-hCG (1st/2nd trimester) Low AFP (1st/2nd trimester) Low oestriol (2nd trimester) High inhibin (2nd trimester) ```

Question 29

What prenatal tests are used to diagnose chromosomal abnormalities?

Answer 29

Amniocentesis and CVS

Question 30

What is the 'combined test' used to screen for down syndrome?

Answer 30

US and blood test (PAPPA and beta-hCG)

Question 31

What are some central nervous system structural abnormalities?

Answer 31

Neural tube defects, ventriculomegaly and akinesia

Question 32

What are neural tube defects?

Answer 32

The result of failure of closure of the neural tube, neural tissue is often exposed, allowing degeneration

Question 33

What is an example of a well-known neural tube defect?

Answer 33

Spina bifida

Question 34

What can the mother take to reduce the risk of neural tube defects?

Answer 34

0.4mg/day folic acid

Question 35

What is ventriculomegaly?

Answer 35

Enlargement of a ventricle(/s), particularly the lateral ventricle. Prognosis depends on the severity and cause

Question 36

What medical in utero therapies are available?

Answer 36

Steroids to mature lungs Antiarrhythmic drugs NSAIDs for polyhydramnios

Question 37

What examples of abdominal wall structural defects are there?

Answer 37

Exomphalos and gastroschisis

Question 38

What is exomphalos?

Answer 38

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

Question 39

What is gastroschisis?

Answer 39

Congenital defect in the anterior abdominal wall just lateral to the umbilical cord Rarely associated with other abnormalities. >90% survive after postnatal surgery

Question 40

What is a diaphragmatic hernia?

Answer 40

The abdominal contents herniate into the chest, causing pulmonary hypoplasia.

Question 41

What is polyhydramnios?

Answer 41

Liquor volume increased. Normal volume varies with gestation, but deepest liquor pool >10cm generally considered abnormal

Question 42

What are the causes of polyhydramnios?

Answer 42

``` Idiopathic Fetal infection Rhesus isoimmunisation Maternal disorders (DM, renal failure) Duodenal atresia Twins Fetal anomaly (Down, Edward) Fetal cardiac failure ```

Question 43

What are the clinical features of polyhydramnios?

Answer 43

Maternal discomfort. Large for dates, taut uterus, fetal parts difficult to palpate

Question 44

What are the complications of polyhydramnios?

Answer 44

Preterm labour, maternal discomfort, abnormal lie and malpresentation

Question 45

How would you treat polyhydramnios?

Answer 45

NSAIDs to reduce fetal urine output

Question 46

List 5 complications of amniocentesis.

Answer 46

1. Preterm labour and delivery 2. Chorioamnionitis 3. Fetal respiratory distress 4. Fetal trauma 5. Red cell alloimmunisation in rhesus negative pregnancies 6. Risk of miscarriage

Question 47

List 5 causes of oligohydramnios.

Answer 47

1. premature rupture of membranes 2. fetal renal problems e.g. renal agenesis 3. intrauterine growth restriction 4. post-term gestation 5. pre-eclampsia