2.3 Ante- And Postnatal Screening Flashcards
What is the purpose of antenatal screening
To identify the risk of a disorder so that further tests and a prenatal diagnosis may be offered.
What are the two types of antenatal screening test
Ultrasound imagining and biochemical tests
What happens in ultrasound imaging
An ultrasound scanner is help up against a pregnant woman’s abdomen and picks up high frequency sounds and converts them to a ultrasound image
What are the two types of ultra sound scans
Dating scan and anomaly scan
When can a dating scan be offered
8-14 weeks
When can an anomaly scan be offered
18 - 21 weeks
What does a dating scan do
Determines the stage of the pregnancy and calculates the date when the baby is due
What abnormalities can be detected in a dating scan
Neural tube defects such as spina bifida
How can Down’s syndrome be screened for in a dating scan
Combined with a blood test and measuring of the the fluid at the back of the baby’s neck
What does an anomaly scan allow
Checks to be made for the presence of any physical abnormalities e.g. a clefts lip
What can changes be detected by
Biochemical tests
How are some medical conditions identified
By the presence of certain marker chemicals in the blood and urine.
What do high levels of HCG show
That a foetus has Down’s syndrome
To monitor the health of the mother and the foetus what tests should be taken
Alpha fetoprotein, renal/liver function, thyroid function
Why would a false positive result
If a marker chemical was measured at the wrong time - could diagnose a child with condition it doesn’t have
Why would a false negative result
Suggests a foetus doesn’t have a condition when it does - so time chosen for biochemical tests has to be closely synchronised with data from ultrasound scans
What is a diagnostic test
A definitive test which shows whether a developing foetus actually has the condition.
Why would diagnostic tests be offered
Family history of genetic disorders, of the woman belongs to a high risk category or if there is evidence of a potential problem
What is a karyotype
A visual representation of an individuals chromosome complement displaying number of chromosomes, arrangement, size and structure for analysis.
What are the two types of diagnostic test
Amniocentesis and chorionic villus sampling
What is Down’s syndrome caused by
An extra chromosome 21 in EACH CELL
What does amniocentesis do
Access whether an unborn baby could develop or is developing a serious genetic condition
When is amniocentesis carried out
Weeks 14 - 16
Describe the process of amniocentesis
The removing of amniotic fluid which surround the foetus. This fluid has foetal cells then collected from it, cultured and then examined under a microscope
What are advantages of amniocentesis
Prenatal diagnosis possible and defects neural tube defects
What are disadvantages of amniocentesis
Gives results later in pregnancy and small risk of miscarriage
What is chorionic villus sampling
A second diagnostic test offered to check for genetic disorders
Describe the process of chorionic villus sampling
Removal of a small sample of cells from an area of the placenta called chorionic villi. Carried out under guidance of ultrasound scanner so nothing enters amniotic fluid or touches the baby. The sample of cells are then cultured, stained and a karyotype is produced.
What are advantages of chorionic villus sampling
Gives results earlier in pregnancy and prenatal diagnosis possible
What are disadvantages of chorionic villus sampling
Higher risk of miscarriage and doesn’t detect neural tube defects
When does chorionic villus sampling happen
11 - 14 weeks
What are the four types of blood groups
A, B, AB, and O
What does your blood contain
Antigens and antibodies
What antigens do each of the blood groups have
A - a antigens
B - b antigens
AB - a & b antigens
O - no a or b antigens
What antibodies do each of the blood groups have
A- b antibodies
B - a antibodies
AB - no a or b antibodies
O - a & b antibodies
What blood group is the universal donor
O
What blood group is the universal recipient
AB
In what situation of birth would there be a serious problem with blood
If a rhesus negative mother has a rhesus positive child and at birth the child’s blood comes into contact with the mothers immune system.
What is the next problem
If the rhesus negative mother has a second rhesus positive child
What is postnatal tests
Screening tests offered to new born babies
When do postnatal tests occur
First 6 - 8 weeks
What are some postnatal screening tests
Physical examination, hearing screening test, blood spot (heel prick) test
What are the benefits of postnatal screening
Early treatment can improve their health and prevent severe disability or death
What is an example of a metabolic disorder
PKU
What is PKU
An inborn error of metabolism
What does having PKU mean
The body cannot turn food into energy
What is PKU caused by
A genetic mutation in the PAH gene (because enzymes are proteins)
What happens as a result of PKU in babies
They can’t break down the amino acid phenylalanine which builds up in the blood and brain
What is the treatment for PKU
A restricted diet containing minimum quantity of phenylalanine
What is a consequence of untreated PKU
Mental deficiency
What does genetic counselling involve
Gathering information about the occurrence of genetic conditions from an individuals family members
What does genetic counselling provide
Support, information and advice
What are all the chromosomes called (excluding sex chromosomes)
Autosomes
Why may genetic counselling be carried out
Diagnosing a person with a genetic condition, working out the risk of someone developing a condition or determining whether someone is a carrier of a genetic condition
Why are family tress only expected to work out the RISK of inheriting a genetic condition
Fertilisation is a random process
What are the patterns of inheritance
Autosomal recessive, autosomal dominant, incomplete dominance and sex linked recessive
What is an example of autosomal recessive inheritance
Cystic fibrosis
What are the features of a autosomal recessive pedigree chart
Trait is expressed very rarely, it skips generations, expressed in some offspring of marriage between cousins and males and females equally affected
What is an example of autosomal dominant inheritance
Huntington’s chorea
What are the features of an autosomal dominant inheritance
Trait appears in every generation, each sufferer has an affected parent, doesn’t skip generations, males and females affected equally
What is an example of autosomal incomplete dominance
Sickle cell trait
What are features of autosomal incomplete inheritance
The fully expressed form occurs rarely, partly expressed form occurs frequently, males and females affected equally
What is an example of sex linked recessive inheritance
Male pattern baldness
