Ante and Postnatal Screening

Question 1

Ante and Postnatal Screening

Answer 1

A variety of techniques can be used to monitor the health of the mother and developing fetus and baby.

A screening test is one that is used to detect signs and symptoms associated with a certain condition or disorder.

If signs are found, the probability that the individual is suffering the condition can be assessed as a degree of risk.

Question 2

Antenatal

Answer 2

Antenatal (pre-birth, in pregnancy) screening identifies the risk of a disorder so that further tests and a prenatal diagnosis can be offered.

Question 3

Postnatal screening

Answer 3

Postnatal screening is after birth screening which can diagnose metabolic or genetic disorders in the baby.

Question 4

Antenatal Screening Techniques

Answer 4

Ultrasound imaging
Biochemical marker tests
Blood/Urine Tests
Diagnostic Tests

Question 5

Dating Scan(antenatal)

Answer 5

Carried out at 8 to 14 weeks, where they determine the stage of the pregnancy and estimate the date of delivery

Question 6

Anomaly Scan(antenatal)

Answer 6

-Carried out at 18-20 weeks which may detect serious physical abnormalities
-Organs are checked with location as well as measurements of femur etc.

Question 7

Biochemical Testing(blood and urine tests)(antenatal)

Answer 7

-Routine blood and urine tests are carried out throughout pregnancy to monitor the concentrations of marker chemicals.
-The results of these tests are used alongside dating scans to check whether the concentration of marker chemicals follow the typical changes expected during a pregnancy.
-when baby is got down syndrome hCG levels remain high after 10 weeks
-An atypical chemical concentration can lead to diagnostic testing to determine if the fetus has a medical condition

Question 8

False Positive Results(antenatal)

Answer 8

-Measuring a chemical at the wrong time could lead to a false positive result.
-results indicates that a person has a specific condition when the person actually does not have it.

Question 9

What are the consequences of FALSE POSITIVE RESULTS

Answer 9

-Causes anxiety
-Additional diagnostic tests carry risk of increased miscarriage
Parents may make a decision to terminate when it is not necessary.

Question 10

Diagnostic Testing(antenatal)

Answer 10

is a definitive test that produces results that can be used to establish without doubt if the person is suffering from the condition or not.

Question 11

When is a woman offered Diagnostic Testing

Answer 11

-Potential problems arise from early screening.
-There is family history of a harmful genetic disorder.
-She already belongs to a high risk category (i.e. women over 35 for risk of down syndrome)

Question 12

Karyotype

Answer 12

-A person’s karyotype shows an individual’s chromosomes arranged as homologous pairs
-Cells from tissue samples can be cultured to obtain sufficient cells to produce a karyotype to diagnose a range of conditions.

Question 13

What methods are used to obtain karyotype(antenatal)

Answer 13

Amniocentesis
Chorionic villus sampling

Question 14

Amniocentesis(antenatal)

Answer 14

-Carried out at 14-16 weeks.
-Fetal cells drawn in from
amniotic fluid.
-Cells cultured, stained and examined under a microscope.
-Chromosome complement photographed in a karyotype.
-Results can take up to 2 weeks.(longer
0.5% miscarriage risk(lower)

Question 15

Chorionic villus sampling(antenatal)

Answer 15

-Carried out as early as 8 weeks.
-Cells taken from the placenta.
-Cells cultured and used for karyotyping.
-Results obtained quicker than amniocentesis.
2% miscarriage risk.(higher)

Question 16

Advantages of CVS

Answer 16

-Carried out earlier than Amniocentesis
-Results obtained quicker than amniocentesis

Question 17

Disadvantages of CVS

Answer 17

Greater risk of miscarriage

Question 18

Advantages of Amniocentesis

Answer 18

Lower risk of miscarriage

Question 19

Disadvantages of Amniocentesis

Answer 19

-Carried out later than CVS
-Results obtained more slowly than for CVS

Question 20

Decision Making for CVS and Amniocentesis

Answer 20

In deciding to proceed with these tests, the element of risk will be assessed, as will the decisions the individuals concerned are likely to make if a test is positive.

Question 21

Post natal screening – diagnostic testing for PKU

Answer 21

PKU = phenylketonuria
Metabolic disorder caused by a substitution mutation.

If PKU is not detected soon after birth it will leads to a build up of toxins which affect brain cells and limits mental development.

In the UK, babies are routinely checked for excess phenylalanine in the first few days of birth using a heel-prick test.

Question 22

How are PKU sufferers treated

Answer 22

-Individuals with high levels of phenylalanine are placed on a restricted diet
-Thislow-protein dietwould completely avoid high-proteinfoods (such as meat, eggs and dairy products) and controls the intake of many other foods, such as potatoes and cereals.

Question 23

Why is there a build-up of phenylalanine?

Answer 23

PKU is caused by a substitution mutation that means the enzyme which converts phenylalanine to tyrosine is non-functional.

Question 24

Human Pedigrees

Answer 24

-Post natal genetic disorders can be either categorized as sex-linked or autosomal.
-Sex Chromosomes - pair 23 , X or Y
-Autosomes – all other chromosomes

Question 25

Genetic Counselling

Answer 25

-Construction of a family tree (pedigree chart) is carried out by a genetic counsellor.
-This is done when information and advice are required by a couple who are worried about possibly passing on a genetic disorder onto their children.

Question 26

How do you know if you are at risk of a particular genetic disorder

Answer 26

Identification of DNA sequences that increase risk of particular diseases or abnormalities can be identified by genetic screening

Question 27

Autosomal recessive inheritance e.g. Cystic fibrosis

Answer 27

A geneticist recognises such a trait since:
Trait relatively rare
Trait may skip generations
Trait in some offspring of a consanguineous marriage (cousins)
Males and females affected in equal number

Question 28

What rules does a geneticist apply to a family tree when autosomal recessive

Answer 28

When recessive can add in genotype (as must be homozygous recessive double cc)
Then can work out backwards – as one from each parent etc.

Question 29

Autosomal dominant inheritance e.g. Huntingtons chorea

Answer 29

A geneticist recognises such a trait since:
Trait in every generation
Each sufferer has affected parent
When a branch of the tree does not express trait, trait fails to reappear in future
Males and females affected in equal number

Question 30

What rules does a geneticist apply to a family tree when autosomal dominant

Answer 30

-All non-suffers must be homozygous recessive double hh
-Sufferers are homozygous dominant (HH) or heterozygous (Hh)

Question 31

Autosomal incomplete dominant inheritance

Answer 31

-Neither allele is completely dominant over the other.
-A heterozygous individual will have a blend of the two homozygous types.

Question 32

Autosomal incomplete dominant inheritance e.g. Sickle cell anaemia(geneticist)

Answer 32

A geneticist recognises such a trait since:
Full expression rare
Partial expression more frequent
Full sufferer has parents with partial condition
Males and females affected in equal number

Question 33

What rules does a geneticist apply to a family tree when autosomal incomplete dominant

Answer 33

-All non-suffers must be homozygous for one incompletely dominant allele (e.g. AA)
-Suffers are homozygous of other dominant allele (e.g. SS)
-Partial must have one each (e.g. AS)

Question 34

Sex linked recessive trait e.g. Haemophilia

Answer 34

A geneticist recognises such a trait since:
Many more males affected than females
No sons of an affected male shows the trait
Some grandsons may have trait

Question 35

What evidence from the family tree confirms the condition is not sex-linked

Answer 35

affected male parent could not have got the condition from his dad as the dad woud have given him the Y chromosome