2.4 Ante&Postnatal Screening

Question 1

What is Antenatal screening?

Answer 1

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

Question 2

What is ultra sound imaging?

Answer 2

Ultrasound scanner is held against woman’s abdomen & picks up high frequency sounds which bounced off foetus and is converted to an ultrasound image

Question 3

What times are ultrasound scans given during pregnancy?

Answer 3

8-14 weeks to produce dating scan to determine stage of pregnancy
18-20 weeks to produce anomly scan to check for presence of serious physical abnormalities in the foetus

Question 4

Why are biochemical tests carried out?

Answer 4

To assess risk of chromosomal abnormalities in the foetus taking into consideration the mothers age

Question 5

Blood & urine tests are used to

Answer 5

Monitor renal, liver & thyroid functions & other biochemical changes

Question 6

How do false positives/negatives happen?

Answer 6

If a marker chemical was measured at wrong time & found to be high this would be a false positive & if was low this would be a false negative

Question 7

When should human chronic gonadotropin be high?

Answer 7

Weeks 6-10 if it remains high the baby has Down syndrome

Question 8

How is time chosen for biochemical tests?

Answer 8

Time is synchronised with ultrasound dating scans

Question 9

What is a screening test?

Answer 9

To dectect signs & symptoms of conditions

Question 10

What is a diagnostic test?

Answer 10

Definitive meaning it establishes if a specific condition is present

Question 11

When are diagnostic tests offered?

Answer 11

If results from screening tests show evidence of a potential problem
Family history of a genetic disorder
Woman belongs to high risk category eg over 35.

Question 12

Why do older woman have a higher risk of down syndrome babies?

Answer 12

Germline cells are more prone to having an extra copy of chromosome 21.

Question 13

Examples of diagnostic tests are

Answer 13

Amniocentesis

CVS- Chronic Villus sampling

Question 14

Amniocentesis is carried out when?

Answer 14

14-16 weeks

Question 15

What does amniocentesis involve?

Answer 15

Withdrawing a little amniotic fluid containing fetal cells using a syringe to arrange chromosomes into a karyotype to detect chromosomal abnormalities

Question 16

Amniocentesis increases the risk of what?

Answer 16

Miscarriage

Question 17

What does CVS involve

Answer 17

Taking a sample of placenta cells using a testube inserted into the reproductive tract. Cells are cultured and uses for karyotyping

Question 18

When is it carried out?

Answer 18

Can be carried out at 8 weeks pregnant

Question 19

Downside to CVS

Answer 19

Higher risk of miscarriage ( higher than amniocentesis)

Question 20

What is a karyotype

Answer 20

A display of a persons chromosome compliment with chromosomes arranged in homologous pairs.

Question 21

Karyotype of Down syndrome

Answer 21

Extra copy of chromosome 21

Question 22

Down syndrome is characterised by

Answer 22

Learning difficulties, distinct physical features

Question 23

Down syndrome occurs in

Answer 23

1 in 800 live births

Question 24

Karyotype of someone with turners syndrome

Answer 24

Missing an X chromosome

Question 25

Individuals affected by turners syndrome

Answer 25

Always female, short, infertile as ovaries don’t develop, fail to develop secondary sexual characteristics at puberty

Question 26

Turners syndrome Occurs in

Answer 26

1 in 2500 female births

Question 27

Karyotype of someone with Klinefelters syndrome

Answer 27

Extra sex chromosome eg XXY

Question 28

Individual affected with klinefelters syndrome

Answer 28

Always male, has male sex organs but infertile due to small testes, very small, can’t produce sperm

Question 29

Klinefelter syndrome occurs in

Answer 29

1 in 1000 male live births

Question 30

Karyotype of someone with Edwards syndrome

Answer 30

Extra copy of chromosome 18

Question 31

Individuals affected with Edwards syndrome

Answer 31

Unusual skull shape, small chin, heart and kidney malformations, delay with aspects of development
Few survive

Question 32

Autosomal recessive means

Answer 32

All sufferers are homozygous and recessive (rr)

Question 33

Who does Autosomal recessive traits affect?

Answer 33

Male and female are equally affected

Question 34

Autosomal recessive trait can skip generations because

Answer 34

Dominant genotype will take over

Question 35

Autosomal dominant pattern affects

Answer 35

Homozygous dominant or heterozygous

Question 36

Autosomal dominant affects every generation

Answer 36

Every sufferer has an affected parent

Question 37

Who is affected by autosomal dominant

Answer 37

Male and females are affected equally

Question 38

What genes are involved in an Autosomal condition?

Answer 38

Genes 1-22

Question 39

What is Autosomal incomplete dominance

Answer 39

When one allele of a gene is not completely dominant over another allele

Question 40

What chromosome are involved in sex linked conditions

Answer 40

Chromosomes 23 (X & Y chromosomes)

Question 41

Females sex chromosomes consist of

Answer 41

Two X chromosomes (XX)

Question 42

Males sex chromosomes consist of

Answer 42

One X and one Y (XY)

Question 43

Why can males not be carriers of traits they aren’t affected by?

Answer 43

Because every X chromosome has sex linked genes Y chromosomes do not so males have one genotype from each X chromosome but non on the Y

Question 44

What are the genotypes of a normal female, carrier female , affected female, normal male and affected male in a sex linked recessive condition?

Answer 44

Normal female- XCXC
Carrier- XCXc 
Affected - XcXc
Normal male- XCY
Affected male- XcY