2.4. Ante- and Postnatal Screening Flashcards
What is antenatal screening?
Assessing the mother and the fetus’ health and checking the fetus for abnormalities before birth.
Describe ultrasound imaging and when do they take place in the pregnancy?
Scans which scan for pregnancy stage and due date. The first scan is carried out at 8-14 weeks (this determines birth date). A second scan takes place at 18-20 weeks which looks for anomalies.
What type of antenatal screening helps screen for medical conditions?
Diagnostic testing.
Name the two main diagnostic tests.
Amniocentesis and chorionic villus sampling (CVS).
Describe the process of amniocentesis.
Amniotic fluid is withdrawn from the amniotic sac through a needle which is then given biochemical tests and is karyotyped.
Describe the process of chorionic villus sampling.
A suction tube is inserted through the cervix and fetal cells are extracted which are then given biochemical tests and are karyotyped.
What are disadvantages of diagnostic tests?
They both carry a small risk of miscarriage.
What is a karyotype?
An image of an individual’s chromosomes arranged in pairs. They are used to identify anomalies in terms of the numbers or structures of chromosomes.
What would happen if a mother was rhesus negative and the fetus was rhesus positive?
Red blood cells from the fetus cross the placenta and can trigger the release of rhesus antibodies from the mother. These antibodies can cross back into the fetal blood and cause the blood to clot. This can be treated by giving the mother anti-rhesus antibodies.
What is phenylketonuria (PKU)?
An inborn error of metabolism caused by an autosomal recessive disorder. It involves gene mutation when encoding the enzyme that converts phenylalanine into tyrosine. Individuals with PKU cannot metabolise phenylalanine. The phenylalanine converts into phenylpyruvate which can negatively affect a baby’s mental development. Treatments include a restricted diet with no phenylalanine.
Give a definition of postnatal screening.
Check-ups that happen after birth. This is to detect medical conditions and abnormalities.
If a disorder is an autosomal recessive disorder, what genotype would someone need to have to have this disorder?
cc, dd, ee etc. (both lower case)
If a disorder is an autosomal dominant disorder, what genotype would someone need to have this disorder?
CC, DD, EE, Cc, Dd, Ee (at least one capital)
What is different about autosomal incomplete dominance?
If their genotype is CC, DD, EE etc. they are severely affected, if their genotype is Cc, Dd, Ee etc. they are mildly affected.
Give an example of an autosomal incomplete dominance disorder.
Sickle cell disease, mildly affected people get the sickle cell trait while severely affected people get sickle cell anaemia.
