Antenatal And Postnatal Screening

Question 1

What is antenatal screening?

Answer 1

A method of detecting potential issues with an embryo or fetus before birth

It is used when there is a family history of a genetic condition.

Question 2

What are the majority of techniques used in antenatal screening?

Answer 2

• Non-invasive techniques
• Used during the first six months of pregnancy

The number of conditions that can be detected before birth is increasing.

Question 3

What can antenatal testing reveal about the developing embryo?

Answer 3

• Sex of the embryo
• Blood group
• Risk of genetic disorder
• Prenatal diagnosis of disease
• Delivery date

These tests help monitor the health of the mother-to-be and her developing fetus.

Question 4

What is the purpose of ultrasound imaging in pregnancy?

Answer 4

To create an image of the fetus in the uterus using high-frequency sound waves

This technique was developed in Scotland.

Question 5

How many ultrasound scans are women given during pregnancy?

Answer 5

Two scans

A dating scan and an anomaly scan.

Question 6

When does the dating scan take place during pregnancy?

Answer 6

Between 8 and 14 weeks

It determines the stage of pregnancy and calculates the expected delivery date.

Question 7

What is the purpose of the anomaly scan?

Answer 7

To detect serious physical abnormalities in the fetus

This scan takes place between 18 and 20 weeks.

Question 8

What additional tests are used alongside dating scans?

Answer 8

• Biochemical tests
• Chemical markers such as proteins

These markers vary in concentration during pregnancy.

Question 9

What is the purpose of biochemical testing during pregnancy?

Answer 9

To monitor the concentrations of proteins produced by the placenta

Blood and urine tests are routinely carried out throughout pregnancy.

Question 10

What can unusually low or atypical levels of a particular protein marker molecule indicate?

Answer 10

Potential identification of a fetus with Down’s syndrome

This is part of diagnostic testing to investigate medical conditions.

Question 11

Why is timing important in biochemical tests during pregnancy?

Answer 11

Measuring a chemical at the wrong time could lead to a false positive result

Dating scans may help ensure appropriate timing of tests.

Question 12

What are the two main types of diagnostic tests mentioned?

Answer 12

• Amniocentesis
• Chorionic villus sampling (CVS)

These tests involve taking samples from the placenta, amniotic fluid, or fetal blood.

Question 13

What is amniocentesis used for?

Answer 13

To diagnose potential birth abnormalities by examining cells in the amniotic fluid

It is performed between the fifteenth and twentieth weeks of pregnancy.

Question 14

Who is typically offered amniocentesis?

Answer 14

Women over the age of 35 or those with prior blood tests indicating potential abnormalities

A small sample of amniotic fluid is removed for genetic analysis.

Question 15

What does the amniotic fluid contain that is useful for genetic analysis?

Answer 15

Cells shed by the fetus

These cells are used to detect possible defects in brain or spinal cord development.

Question 16

What is chorionic villus sampling used for?

Answer 16

To diagnose potential congenital abnormalities by examining cells from the placenta

This procedure takes place between the tenth and thirteenth weeks of pregnancy.

Question 17

When is chorionic villus sampling typically performed?

Answer 17

Between the tenth and thirteenth weeks of pregnancy

It is offered to women with a family history of genetic conditions or previous abnormal blood tests.

Question 18

What is the method of chorionic villus sampling?

Answer 18

• A long flexible tube is inserted through the vagina into the cervix
• Guided towards the placenta
• A small sample of tissue is taken from the placenta

This sample is used for genetic analysis.

Question 19

What is a key limitation of chorionic villus sampling compared to amniocentesis?

Answer 19

Cannot detect possible defects in the development of the brain or spinal cord

Both tests carry a risk of miscarriage.

Question 20

What is the estimated risk of miscarriage for chorionic villus sampling?

Answer 20

1-2%

The risk for amniocentesis is approximately 1% after the fifteenth week of pregnancy.

Question 21

What can cells taken by chorionic villus sampling be used to produce?

Answer 21

A karyotype

A karyotype is a visual record of chromosomes arranged as homologous pairs.

Question 22

What genetic condition can be diagnosed by examining abnormalities in the karyotype?

Answer 22

Down’s syndrome

Abnormalities in chromosome numbers and shapes can indicate genetic conditions.

Question 23

True or false: Chorionic villus sampling carries a lower risk of miscarriage than amniocentesis.

Answer 23

FALSE

Chorionic villus sampling carries a higher risk of miscarriage compared to amniocentesis.

Question 24

In deciding to proceed with karyotyping, what must be assessed?

Answer 24

The element of risk to the developing baby

Individuals are also advised to consider their options if test results are positive.

Question 25

What is the purpose of **pedigree charts** in genetics?

Answer 25

To reveal both the phenotypes and genotypes of family members ## Footnote Useful for families at high risk of genetic conditions such as albinism or Huntington's disease.

Question 26

Four important **inheritance patterns** can be shown using pedigree charts. Name one.

Answer 26

Defective recessive autosomal inheritance ## Footnote This pattern is characterized by specific traits and behaviors in genetic conditions.

Question 27

What is a characteristic of **defective recessive autosomal inheritance**?

Answer 27

* Expressed relatively rarely * Usually skips generations * Affects both males and females equally * Requires homozygous recessive individual * Can be carried by heterozygous individual * Can result from two unaffected heterozygous parents ## Footnote This inheritance pattern is important for understanding genetic disorders.

Question 28

True or false: A **defective recessive autosomal disorder** can be expressed in an individual who is heterozygous.

Answer 28

FALSE ## Footnote The affected individual must be homozygous recessive to express the disorder.

Question 29

In a pedigree chart, what does a **carrier** represent?

Answer 29

An individual who is heterozygous for a defective recessive allele ## Footnote Carriers do not express the disorder but can pass it to offspring.

Question 30

What is the significance of **tracking genetic conditions** over several generations?

Answer 30

It provides increased knowledge for making decisions about having children ## Footnote Helps predict the likelihood of inheriting genetic traits.

Question 31

Fill in the blank: A pedigree chart can be used to track how a genetic condition is expressed over several _______.

Answer 31

generations ## Footnote This tracking is crucial for understanding inheritance patterns.

Question 32

What type of inheritance pattern is characterized by traits that **skip generations**?

Answer 32

Defective recessive autosomal inheritance ## Footnote This pattern often leads to affected individuals arising from unaffected parents.

Question 33

What is a **defective autosomal dominant allele**?

Answer 33

* Affects both males and females in equal numbers * Means anybody affected will have an affected parent * No longer appears in future generations if a branch of the pedigree does not show the disorder * Results in all non-affected individuals being homozygous recessive * Means anybody affected is either double dominant or heterozygous ## Footnote Example disorder: Huntington's disease.

Question 34

In the **homozygous state**, what does a defective autosomal dominant allele produce?

Answer 34

Maximum expression of the phenotype ## Footnote Rarely expressed maximally as the two alleles present are incompletely dominant over each other.

Question 35

In the **heterozygous state**, what does a defective autosomal dominant allele produce?

Answer 35

Reduced expression of the phenotype ## Footnote This can lead to varying degrees of severity in the expression of the disorder.

Question 36

What is a **defective sex-linked recessive allele**?

Answer 36

* Affects many more males than females * Not transmitted to a male from his affected father * Needs an individual to be homozygous if they are female * Will be expressed in a male who has one copy of the defective allele * Will not be expressed in a homozygous unaffected male or a heterozygous female ## Footnote Example disorder: Hemophilia.

Question 37

True or false: A **defective sex-linked recessive allele** is usually transmitted from an affected father to his son.

Answer 37

FALSE ## Footnote Affected males do not transmit the disorder to their sons.

Question 38

What does it mean if a female is a **carrier** of a defective sex-linked recessive allele?

Answer 38

She is usually unaffected but can pass the allele to her offspring ## Footnote All daughters of affected fathers will either be carriers or affected themselves.

Question 39

What is **postnatal screening**?

Answer 39

The use of diagnostic testing to check for any abnormalities in a baby after it is born ## Footnote One important use of screening is to check for metabolic errors such as phenylketonuria (PKU).

Question 40

What condition is commonly screened for in newborns in the UK?

Answer 40

Phenylketonuria (PKU) ## Footnote Babies are tested by taking a blood sample from the heel.

Question 41

Phenylketonuria (PKU) is caused by a mutation in what type of allele?

Answer 41

Autosomal recessive allele ## Footnote This mutation affects the enzyme that converts phenylalanine to tyrosine.

Question 42

What happens if a baby is diagnosed with **phenylketonuria (PKU)**?

Answer 42

A restricted diet is prescribed ## Footnote The diet contains low levels of phenylalanine and avoids certain foods like cereals and potatoes.

Question 43

What is the purpose of the restricted diet for a baby diagnosed with PKU?

Answer 43

To ensure normal brain function development ## Footnote The diet is usually continued into adulthood.

Question 44

In PKU, what is the consequence of the enzyme not functioning?

Answer 44

Phenylalanine is not converted to tyrosine ## Footnote This leads to the accumulation of phenylalanine, which can cause brain damage.