Ante and Postnatal Screening Flashcards
Ante and Postnatal Screening
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.
Antenatal
Antenatal (pre-birth, in pregnancy) screening identifies the risk of a disorder so that further tests and a prenatal diagnosis can be offered.
Postnatal screening
Postnatal screening is after birth screening which can diagnose metabolic or genetic disorders in the baby.
Antenatal Screening Techniques
Ultrasound imaging
Biochemical marker tests
Blood/Urine Tests
Diagnostic Tests
Dating Scan(antenatal)
Carried out at 8 to 14 weeks, where they determine the stage of the pregnancy and estimate the date of delivery
Anomaly Scan(antenatal)
-Carried out at 18-20 weeks which may detect serious physical abnormalities
-Organs are checked with location as well as measurements of femur etc.
Biochemical Testing(blood and urine tests)(antenatal)
-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
False Positive Results(antenatal)
-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.
What are the consequences of FALSE POSITIVE RESULTS
-Causes anxiety
-Additional diagnostic tests carry risk of increased miscarriage
Parents may make a decision to terminate when it is not necessary.
Diagnostic Testing(antenatal)
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.
When is a woman offered Diagnostic Testing
-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)
Karyotype
-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.
What methods are used to obtain karyotype(antenatal)
Amniocentesis
Chorionic villus sampling
Amniocentesis(antenatal)
-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)
Chorionic villus sampling(antenatal)
-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)
Advantages of CVS
-Carried out earlier than Amniocentesis
-Results obtained quicker than amniocentesis
Disadvantages of CVS
Greater risk of miscarriage
Advantages of Amniocentesis
Lower risk of miscarriage
Disadvantages of Amniocentesis
-Carried out later than CVS
-Results obtained more slowly than for CVS
Decision Making for CVS and Amniocentesis
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.
Post natal screening – diagnostic testing for PKU
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.
How are PKU sufferers treated
-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.
Why is there a build-up of phenylalanine?
PKU is caused by a substitution mutation that means the enzyme which converts phenylalanine to tyrosine is non-functional.
Human Pedigrees
-Post natal genetic disorders can be either categorized as sex-linked or autosomal.
-Sex Chromosomes - pair 23 , X or Y
-Autosomes – all other chromosomes
Genetic Counselling
-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.
How do you know if you are at risk of a particular genetic disorder
Identification of DNA sequences that increase risk of particular diseases or abnormalities can be identified by genetic screening
Autosomal recessive inheritance e.g. Cystic fibrosis
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
What rules does a geneticist apply to a family tree when autosomal recessive
When recessive can add in genotype (as must be homozygous recessive double cc)
Then can work out backwards – as one from each parent etc.
Autosomal dominant inheritance e.g. Huntingtons chorea
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
What rules does a geneticist apply to a family tree when autosomal dominant
-All non-suffers must be homozygous recessive double hh
-Sufferers are homozygous dominant (HH) or heterozygous (Hh)
Autosomal incomplete dominant inheritance
-Neither allele is completely dominant over the other.
-A heterozygous individual will have a blend of the two homozygous types.
Autosomal incomplete dominant inheritance e.g. Sickle cell anaemia(geneticist)
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
What rules does a geneticist apply to a family tree when autosomal incomplete dominant
-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)
Sex linked recessive trait e.g. Haemophilia
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
What evidence from the family tree confirms the condition is not sex-linked
affected male parent could not have got the condition from his dad as the dad woud have given him the Y chromosome
