2.4a : Antenatal & Postnatal screening Flashcards
Antenatal Screening
Identifies the risk of a disorder so that further tests and a prenatal diagnosis can be offered.
Dating Scan
Measures the due date and takes place between 8 and 14 weeks.
Anomaly Scan
May detect serious physical abnormalities and takes place between 18 and 20 weeks.
Blood Tests
Carried out throughout pregnancy to monitor the concentrations of marker chemicals.
False Positive Result
Measuring a chemical in the blood at the wrong time could lead to a false
positive result (this can happen if the dating scan was inaccurate).
Atypical Chemical Concentration
Can lead to diagnostic testing to determine if the foetus has a medical condition.
Diagnostic Testing
Used to diagnose a condition (NOT just the risk of one).
Types of Diagnostic Tests
Amniocentesis and Chorionic Villus Sampling (CVS).
Amniocentesis
When amniotic fluid (which will contain cells from the foetus) is removed from the uterus using a syringe. This has a lower miscarriage risk but is carried out later in the pregnancy.
CVS
When a sample of the chorionic villus (part of the placenta) is removed. This can be carried out earlier in the pregnancy but has a higher risk of miscarriage.
Cells from Samples
Can be cultured to obtain sufficient cells to produce a karyotype to diagnose a range of conditions.
Karyotype
Shows an individual’s chromosomes arranged as homologous pairs.
Postnatal Screening
Offered to all babies to monitor their health.
Phenylketonuria (PKU)
Detected using a diagnostic test (heel prick test) postnatally.
PKU
In PKU a substitution mutation means that the enzyme which converts phenylalanine to tyrosine is non-functional.
PKU is treated by restricting the diet and avoiding phenylalanine.
