Prenatal Testing

Question 1

Prenatal screening

Answer 1

focuses on finding problems among a large population with affordable and noninvasive methods.
Example are – Down syndrome, Blood Borne Virus, USS

Question 2

Prenatal diagnosis

Answer 2

focuses on pursuing additional detailed information once a particular problem has been found, and can sometimes be more invasive.
Example are - amniocentesis and chorionic villus sampling.

Question 3

purpose of prenatal testing

Answer 3

To enable timely medical or surgical treatment of a condition before or after birth
To give the parents the chance to terminate the pregnancy with the diagnosed condition
To give parents the chance to prepare psychologically, socially, financially, and medically for a baby with a health problem or disability, or for the likelihood of a stillbirth.
To organise appropriate fetal surveillance

Question 4

screening in the UK

Answer 4

• Offeredtoallpregnantwomen
• To assess either woman or baby have particular health issue or disability
• Simple tests – Blood test, USS or questionnaire
• Not diagnostic
• Follow on test for diagnosis

Question 5

What kind od blood tests can be performed

Answer 5

• Full blood count
• Blood group and Rhesus state
• Haemoglobinopathies – Thalasemmia and Sickle cell disorder
• Infectious diseases
• Chromosomal disorders – Trisomies ( 21, 18 and 13)

Question 6

Screening for Haemoglobinopathies

Answer 6

• high risk groups
• If woman is carrier then partner testing will be offered - If partner is positive - genetic counselling
• Amniocentesis or CVS – to see if fetus is affected
• Newborn – blood spot screening test

Question 7

Screening for Trisomies

Answer 7

Assess the chance of the baby being born with Down’s syndrome or Edwards’ syndrome or Patau’s syndrome.

Question 8

screening for trisomies, what is the test sensitive to

Answer 8

The test is sensitive for singleton and twin pregnancies , not for any other higher multiple pregnancy.

Question 9

factors that can effect screening for trisomies

Answer 9

Smoking, ethnicity, BMI, age
Assisted pregnancy( donor egg or frozen embryo)

Question 10

Down’s syndrome (Trisomy 21 )

Answer 10

Commonest cause of identifiable learning disability – Usually due to non- disjunction at chromosome 21 at meiosis.
50 % will have a congenital abnormality
80% profound or severe intellectual impairment

Question 11

trisomy 18

Answer 11

Edwards’ syndrome

Question 12

trisomy 13

Answer 12

Patau’s syndrome

Question 13

First trimester combined test

optical time

Answer 13

Optimal time - 11+2 weeks to 14+1 weeks of gestation

Question 14

Detection Rate fro down syndrome in first trimeter

Answer 14

Down’s syndrome detection Rate (DR) is 84%

Question 15

• Edwards’ syndrome detection Rate (DR) is in first trimester

Answer 15

about 85% and False Positive Rate is 0.2%

Question 16

Second Trimester Screening

Answer 16

• Optimal time is 14+2 -20 weeks

Question 17

detection for don syndrome 2nd trimester

Answer 17

Detection rate is 80% and FPR is 3.5%. for Down’s syndrome..

Question 18

detection for Edwards 2nd trimester

Answer 18

• Detection Rate (DR) is about 73% and FPR 0.1% for Edward’s syndrome

Question 19

• If screening for all trisomies, then, woman will receive 2 results:

Answer 19

1 chance of having a baby with Down’s syndrome,

2 combined chance of having a baby with Edwards’ syndrome or Patau’s syndrome.

Question 20

• Women who receive a higher-chance result 1:150 from first or second trimester screening tests, further options are

Answer 20

• no further tests
• a new, more accurate blood screening test called non-invasive
prenatal testing (NIPT)
• diagnostic tests: chorionic villus sampling (CVS) or amniocentesis

Question 21

Non Invasive Prenatal Testing (NIPT) - this is screening and not a diagnostic test

Answer 21

• can be performed from 10 weeks of pregnancy

• The results are given as low or high chance result. If the results are low chance
then no further test is offered.

Question 22

What is NIPT also known as

Answer 22

cell free DNA screening test ( cfDNA) , as cell-free DNA material is
extracted and analysed from maternal blood test.

Question 23

• NIPT is better at finding babies who have

Answer 23

Down’s syndrome than finding babies with Edwards’ syndrome or Patau’s syndrome.

Question 24

Twin pregnancies

Answer 24

• NIPT can be as accurate in identical twin pregnancies as if you were pregnant with one baby.
• NIPT may be less accurate in non-identical twin pregnancies because there are two placentas releasing their own DNA.

Question 25

Diagnostic tests

Answer 25

• These are offered to women who have had a ‘higher- chance’ result from screening.
• These are invasive tests like chorionic villus sampling or amniocentesis.
• Alternatively- a detailed ultrasound scan.

Question 26

Chorionic Villi Sampling CVS

Answer 26

• Fine needle inserted through abdomen and into uterus; or through cervix, & small piece of developing placenta removed
• Done from 11 weeks on wards

Question 27

what does Chorionic Villi Sampling CVS test for

Answer 27

Tests for inherited disorders (cystic fibrosis, sickle cell, thalassemias, muscular dystrophy) and chromosomal disorders

Question 28

ethical issues with Chorionic Villi Sampling CVS

Answer 28

2% risk of miscarriage (also, delay in getting results) infection, heavy bleeding

Question 29

Amniocentesis

Answer 29

• Needle inserted through the abdomen and into amniotic fluid For karotyping if screening tests suggest aneuiploidy
DNA analysis if parents carrier of an identifiable gene
Enzyme assays for inborn errors of metabolism
• Done after 15 weeks

Question 30

Preimplantation Genetic Diagnosis (PGD)

Answer 30

• Offered to couples who are at risk of passing on a genetic disorder
• It involves removing 1 cell from the early embryo (4-8 cell embryo)

Question 31

Huntington’s Disease

Answer 31

• Inherited, late onset, degenerative condition
• Manifests ~ 30-50 yrs •
• 50/50 chance of inheriting it from affected parent

Question 32

Saviour Sibling

Answer 32

Saviour Sibling
• A saviour baby or saviour sibling is a child who is born to provide an organ or cell transplant to a sibling that is affected with a fatal disease, such as cancer or Fanconi anemia, that can best be treated by hematopoietic stem cell transplantation.