Key Area 2.4 - Ante and Postnatal Screening

Question 1

What does antenatal screening do?

Answer 1

Identifies the risk of a disorder so that further tests and a prenatal diagnosis can be offered.

Question 2

What are some common antenatal testing procedures?

Answer 2

Ultrasound scanning
Amniocentesis
Chronic villus sampling
Rhesus antibody testing

Question 3

What can ultrasound scanners be used to produce?

Answer 3

A pregnancy or gestational dating scan, which is used to determine the stage of pregnancy and the date the baby is due.
Anomaly scan - which is used to detect the presence of serious physical problems in the fetus.

Question 4

What are biochemical tests used for?

Answer 4

To decent the normal physiological changes of pregnancy. Measuring a substance at the wrong time could lead to a false positive result.

Question 5

What is diagnostic testing?

Answer 5

Medical conditions can be detected by a range of market chemicals that indicate a condition but need not necessarily be part of the condition

Question 6

What type of diagnostic testing are there?

Answer 6

Amniocentesis

CVS

Question 7

What is amniocentesis?

Answer 7

Amniotic fluid drawn from the amniotic sac. Takes several weeks to culture. Results take longer.

Question 8

What is CVS?

Answer 8

Chronic villus sampling. Gives earlier results. Risk of miscarriage. Sample taken from placenta.

Question 9

Describe rhesus antibody testing.

Answer 9

• Normally a mothers immune system does not attach the fetus despite its different signature of the mother is Rhesus negative and her baby is Rhesus positive.
• However there is a chance of some blood mixing at birth which causes sensitisation to Rhesus antigens.
• The immune system of the mother then makes the anti-D antibodies and memory cells thag wait for a future invader.
• The fetus can be saved by replacing the Rhesus positive blood with Rhesus negative.
• Alternatively the mother can be injected with anti-D factor, just after birth, to destroy the D antigen.

Question 10

What is postnatal screening?

Answer 10

Diagnostic testing used to detect metabolic disorders like PKU which is an inborn error of metabolism.

Question 11

What is PKU?

Answer 11

An inborn error of metabolism. The body can not process excess phenylalanine. If PKU is not detected soon after birth the baby’s mental development is affected. Individuals with high levels of phenylalanine are placed on a restricted diet.

Question 12

What is genetic screening?

Answer 12

Use of pedigree charts to analyse patterns of inheritance in genetic screening and counselling.

Question 13

What can genetic screening be used for?

Answer 13

A pattern of inheritance can be revealed by collecting information about a particular characteristic l from family members and the information used to construct a family tree.

Question 14

Describe autosomal recessive.

Answer 14

Expressed relatively rarely in offspring, affects males and females equally and may skip generations through carriers. E.g. - cystic fibrosis

Question 15

Describe autosomal dominant.

Answer 15

Can be common in a family. It affects males and females equally and individual cannot carry the condition without being affected. E.g - Huntington’s disease.

Question 16

Describe autosomal dominance.

Answer 16

The fully expressed form of the condition is rare, the party expressed form is more common and males and females are affected equally. Carriers have a less severe form of the disease, those with two alleles have the more severe form. E.g - sickle cell disease.

Question 17

Describe sex linked recessive.

Answer 17

Males are more commonly affect than females. Male offspring inherit the condition from their mother. Fathers cannot pass the condition on to their sons and female offspring can only be affect if the father has the condition and the mother is at least a carrier. E.g - haemophilia.