2.4 - Antenatal & Postnatal Screening Flashcards
Why is antenatal screening used?
Antenatal screening is carried out to monitor the health of a pregnant woman and the developing foetus.
What does antenatal screening identify?
Antenatal screening identifies the risk of a disorder so that further tests can be carried out and a prenatal diagnosis can be offered.
What are the three methods of antenatal screening
That we are focusing on
Ultrasound imaging
Biochemical tests
Diagnostic tests
What do ultrasound scans do and how did they do it?
Ultrasound scans use soundwaves to build a picture of the developing fetus in the uterus.
What are the two ultrasound scans that pregnant women are given?
- dating scan
- anomaly scan
When does a dating scan take place
A dating scan takes place between 8 and 14 weeks?
What do dating scans determine?
Dating scans determine the stage of pregnancy and the due date.
What are dating scans used with?
Dating scans are used with tests for marker chemicals which vary normally during pregnancy.
What can anomaly scans detect?
Anomaly scans may detect serious physical abnormalities in the foetus.
It looks in detail at the bones, heart, brain, spinal-cord, face, kidneys and abdomen.
When does an anomaly scan take place?
An anomaly scan takes place between 18 and 20 weeks
What are biochemical tests used for
Biochemical tests are used to detect the normal physiological changes of pregnancy. 
What do biochemical tests include?
These tests include:
- blood pressure
- blood type
- general health checks including routine blood and urine tests
Biochemical tests - what can lead to a false positive result?
Measuring a chemical at the wrong time could lead to a false positive result.
Diagnostic testing - What can an atypical chemical concentration lead to?
An atypical chemical concentration can lead to diagnostic testing to determine if the fetus has a medical condition.
Diagnostic testing - How can medical conditions be detected?
Medical conditions can be detected by a range of marker chemicals that indicate a condition, but may not necessarily be part of the condition.
Diagnostic testing- result of routine screening
As a result of routine screening or for individuals in high risk categories, further tests may be offered
In deciding to proceed with these tests, the element of risk will be assessed as will the decision the individuals concerned are likely to make if a test is positive
Diagnostic testing- further tests possibilities
Amniocentesis
Chronic villus sampling (CVS)
What is a Karyotype produced from
Cells from samples from amniocentesis or CVS can be cultured to obtain sufficient cells to produce a karyotype
What is a karyotype
A karyotype is an image of an individuals chromosomes arranged in homologous pairs
How can karyotypes be used
Karyotypes can be used to diagnose a range of conditions
What is the karyotype used to identify
The karyotype is used to identify anomalies in terms of the numbers or structures of chromosomes
What does amniocentesis involve
Amniocentesis involves in the withdrawal of amniotic fluid containing fetal cells
When is amniocentesis carried out
Amniocentesis as carried out around 14 to 16 weeks of pregnancy
Amniocentesis - cells and how long it takes
Cells are cultured and karyotype examined. The process takes two weeks
What does chorionic villus sampling involve
CVS involves a sample of placental cells being removed. It is carried out eight weeks into pregnancy
CVS disadvantage
Higher risk of miscarriage (1-2%)
CVS advantage
Earlier termination possible
Karyotyping can be performed in the feral cells immediately
What are pedigree chart is used for
Pedigree chart are used to analyse patterns of inheritance in genetic screening and counselling
Genetic screening and counselling – what can happen once the phenotype for a characteristic is known
Once the phenotype for a characteristic is nine and a family tree is constructed most of the genotypes can be determined.
This information is used by genetic counsellors to advise parents of the possibility of passing on a genetic condition to their child
Why are routine blood and urine tests carried out
Routine bloods and urine tests are carried out throughout pregnancy to monitor the concentrations of marker chemicals
What is a carrier
A carrier is a person who carries one copy of the faulty gene but doesn’t show the genetic condition.
However they can pass the gene to their offspring.
Describe fertilisation
Fertilisation is a random process.
What are autosomes
The autosomes are all chromosomes except from the sex chromosomes
What do the sex chromosomes determine
The sex chromosomes are the two chromosomes that determine the sex of an individual
What are the patterns of inheritance
Autosomal recessive
Autosomal dominant
Incomplete dominance
Sex linked recessive
Autosomal recessive inheritance - How often are the expressed
Autosomal recessive traits are expressed rarely and may skip generations
Autosomal recessive inheritance - Are males and females affected equally
Males and females are affected equally
Autosomal recessive inheritance - What are the suffers described as
Homozygous recessive
Autosomal recessive inheritance - Who are not affected
Homozygous dominant individuals are not affected
Autosomal recessive inheritance - Who are carriers
Heterozygous individuals are carriers of the condition. They do not show the condition themselves but they can pass it on to their offspring
Autosomal recessive inheritance - example
Cystic fibrosis
Autosomal dominant inheritance - expressed
Appears in every generation
Autosomal dominant inheritance - How are males and females affected
Males and females are affected equally
Autosomal dominant inheritance - How can sufferers be described
Sufferers can be either homozygous dominant or heterozygous
Autosomal dominant inheritance - What are all non-suffers described as
Homozygous recessive
Autosomal dominant inheritance - What happens when a branch of the family does not express the treat
When a branch of the family does not express the trait it fails to reappear in future generations of the branch
Autosomal dominant inheritance - example
Huntington’s disease
Autosomal incomplete dominance - Describe it
Sometimes the dominant allele may not fully express itself which is known as incomplete dominance
Autosomal incomplete dominance - Are males and females equally affected
Males and females equally affected
Autosomal incomplete dominance - How often does the fully express form of the disorder occur
The fully expressed form of the disorder occurs relatively rarely
Autosomal incomplete dominance - How often is the partially expressed form of the disorder expressed
Partially expressed form of the disorder occurs more frequently than the fully expressed form
Autosomal incomplete dominance - What are nonsufferers described as
Nonsufferers are homozygous for one incompletely dominant allele
Autosomal incomplete dominance - How are sufferers of the fully expressed form of the disorder describe as
Sufferers of the fully expressed form of the disorder are homozygous for the other incompletely dominant allele
Autosomal incomplete dominance - How are sufferers of the partly expressed form described as
Sufferers of the partly expressed form are heterozygous for the two alleles
Autosomal incomplete dominance - example
Sickle cell anaemia
Other than determining sex what are the functions of the sex chromosomes
Although the sex chromosomes are mainly responsible for determining sex they also carry some genes that code for a number of body functions.
These genes are described as sex linked
Explain the differences in size between the X and Y chromosome
There is a difference in size between the X and Y chromosome.
The Y chromosome is shorter and therefore some genes appears
only on the X chromosome.
Sex linked recessive - Compare how males and females are affected
Many more males are affected than females.
This is because the X chromosome will show in the phenotype as there is no dominant allele present to override it.
A female will have another allele on her ex chromosome which, if dominant, would mask the effect of the recessive allele
Sex linked recessive - How do male offspring inherit the condition
Male offspring inherit the condition from their mother.
Sex linked recessive - Why can’t fathers pass the condition to their son
Fathers cannot pass the condition to their son therefore none of the sons of an affected male show the trait
Sex linked recessive - How are sufferers of the trait described
Sufferers of the trait are homozygous recessive
Sex linked recessive - How are non-sufferers of the trait described
Nonsufferers of the trait are homozygous dominant
Sex linked recessive - Who are carriers of the trait
Heterozygous females are carriers
Sex linked recessive condition - example
Haemophilia
What is Pre-implantation genetic diagnosis (PGD)
Pre-implantation genetic diagnosis is a technique that enables people with a specific inherited condition in their family to avoid passing it on to their offspring.
It involves checking the genes of embryos created through IVF for this genetic condition
IVF process
During IVF:
- The embryo is grown in the laboratory for a few days until it consists of around eight cells
- And embryologist Removes one or two of the cells from the embryo and tests them to see if the embryo from which they were removed contains the gene that causes the genetic condition in the family
- Embryos unaffected by the condition or transferred to the womb to allow them to develop.
When does postnatal screening take place
Postnatal screening takes place after birth
What does the purpose of postnatal screening
Postnatal screening aims to detect certain conditions and abnormalities
How can post natal screening be used
Postnatal screening can be used to detect metabolic disorders
Such as phenylketonuria (PKU)
Phenylketonuria (PKU) - What does a substitution mutation mean
In PKU, A substitution mutation means that the enzyme which converts phenylalanine to tyrosine is non-functional.
What happens if PKU is not detected and treated soon after birth
If PKU is not detected and treated soon after birth the child’s mental development is affected.
What happens to individuals born with high levels of phenylalanine
Individuals born with high levels of phenylalanine are placed on a restricted diet
