KA4 - Ante And Postnatal Screening

Question 1

What is antenatal screening?

Answer 1

Antenatal screening identifies the risk of a disorder so that further tests can be carried out and a prenatal diagnosis can be offered

Question 2

What is an ultrasound scan?

Answer 2

Ultrasound scans use sound waves to build a picture of the developing foetus in the uterus

Question 3

What are the 2 different ultrasound scans?

Answer 3

Dating scan

Anomaly scan

Question 4

What is a dating scan?

Answer 4

Dating scans which determine the stage of pregnancy and due date are used with tests for marker chemicals which vary normally during pregnancy

Question 5

When does a dating scan take place?

Answer 5

Between 8-14 weeks

Question 6

What is an anomaly scan?

Answer 6

Anomaly scans may detect serious physical abnormalities in the foetus

Question 7

When does an anomaly scan take place?

Answer 7

Between 18-20 weeks

Question 8

What are biochemical tests?

Answer 8

Routine blood and urine tests are carried out throughout pregnancy to monitor the concentrations of marker chemicals

Question 9

What is diagnostic testing?

Answer 9

An atypical concentration can lead to diagnostic testing to determine if the foetus has a medical condition.

Question 10

As a result of routine screening or for individuals in high risk categories, further tests may be offered. What may these tests include?

Answer 10

Amniocentesis

Chronic villus sampling

Question 11

What is used to produce a karyotype?

Answer 11

Cells from samples from amniocentesis or chronic villus sampling can be cultured to obtain sufficient cells to produce a karyotype

Question 12

What is a karyotype?

Answer 12

A karyotype is an image of an individuals chromosomes arranged in homologous pairs

Question 13

What is a karyotype used to identify?

Answer 13

Anomalies in terms of the numbers or structures of chromosomes

Question 14

Give an account of amniocentesis (4)

Answer 14

• amniocentesis involves the withdrawal of amniotic fluid containing foetal cells
• it is carried out around 14-16 weeks of pregnancy
• cells are cultured and karyotype examined
• the process takes 2 weeks

Question 15

Give an account of chronic villus sampling (5)

Answer 15

• CVS involves a sample of placental cells being removed
• carried out 8 weeks into pregnancy
• higher risk of miscarriage (1-2%)
• earlier termination possible
• karyotyping can be preformed on the foetal cells immediately

Question 16

What is a pedigree chart?

Answer 16

Pedigree charts are used to analyse patterns of inheritance in genetic screening and counselling.

Question 17

How is a pedigree chart used?

Answer 17

The information is used by genetic counsellors to advise parents of the possibility of passing on a genetic condition to their child

Question 18

What is a carrier?

Answer 18

A carrier carries one copy of the faulty gene but doesn’t show the genetic condition. They can however pass the gene to their offspring.

Question 19

What is an autosome?

Answer 19

All chromosomes except from the sex chromosomes

Question 20

What are the sex chromosomes?

Answer 20

The 2 chromosome which determine the sex of an individual

Question 21

Summarise autosomal recessive inheritance

Answer 21

• they may skip generations
• makes and females are equally affected
• all sufferers are homozygous recessive

Question 22

Summarise autosomal dominant inheritance

Answer 22

• appear in every generation
• makes and females are equally affected
• sufferers are homozygous dominant or heterozygous
• sufferers have an affected parent

Question 23

Summarise sex linked recessive

Answer 23

• fathers cannot pass the condition on to their son therefore male offspring must inherit the condition from their mother
• sufferers are homozygous recessive
• nom sufferers are homozygous dominant
• heterozygous females are carrier

Question 24

What is pre implantation genetic diagnosis?

Answer 24

Pre implantation genetic diagnosis enables people with a specific inherited condition in their family to avoid passing it on to their children.

Question 25

What is post natal screening?

Answer 25

Post natal screening can be used to detect metabolic disorders such as PKU (phenylketonuria)

Question 26

What is a substitution mutation in PKU?

Answer 26

In PKU, a substitution mutation means that the enzyme which converts phenylalanine to tyrosine is non functional.

Question 27

What is placed for individuals born with high levels of phenylalanine?

Answer 27

They must be placed on a restricted diet