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Flashcards in Genetics 5 Deck (18)
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1
Q

What is the purpose of the nuchal scan that occurs 10-14 weeks into pregnancy?

A

Date pregnancy, check if twins, check babies development, etc

Assess risk of chromosomal abnormalities

Nuchal scan done by looking at nuchal translucency.

2
Q

What is nuchal translucency (NT)

Used in conjunction with maternal age to detect Downies

A

Measures fluid at the back of the babies neck,

Increased NT (>3mm) could indicate:

  • Chromosomal abnormalities
  • Birth defects
  • Skeletal dysplasia
3
Q

When is prenatal testing arranged?

A
  • If abnormal findings found at nuchal or mid-trimester scan
  • if previous pregnancy affected with a condition
  • if parent is a carrier of a genetic condition or chromosome rearrangement
  • family history of genetic condition
4
Q

What are the 3 types of prenatal tests?

A
  1. Non invasive (ultrasound)
  2. Minimally invasive (maternal blood test/cell free foetal DNA)
  3. Invasive (amniocentesis/Chorionic Villus Sampling)
5
Q

Describe Non invasive prenatal tests.

A

Ultrasound - early/dating scan/High level (/anomaly Scan), usually best from 9 weeks
Foetal MRI - high level anomaly can be diagnostic (cleft lip/limb deformity/cardiac problem), show markers can show other problems

THE NASAL BONE IS A SOFT MARKER

6
Q

Describe a Minimally Invasive Prenatal test

A

-Blood tests for the mum. No foetal risk.

MATERNAL SERUM SCREENING
-detects blood serum markers, tests for increased risk of trisomy 21, 18 and/or neural tube defects

TYPES OF MATERNAL SERUM SCREENING
1. 1st trimester = 11-14 weeks. Done alongside NT measurement. Looks for presence of HCG and PAPP A.

  1. 2nd Trimester - 16-20 weeks, looks for HCG/PAPP A/AFP/uE3 (oestriol)
  2. Nuchal Translucency Measurement - 11-14 weeks

IF FOUND THAT WOMAN AT RISK OF GENETIC DISEASE, INVASIVE PROCEDURES OFFERED

7
Q

What is cell-free Foetal DNA test (cffDNA)?

A

OFFERED ESPECIALLY IF BABY HAS RISK OF HAVING AN X LINKED CONDITION

  • Test done to determine sex of baby
  1. Some foetal DNA is present in maternal blood
  2. Blood test done which isolates baby DNA and looks for Y chromosome
  3. If Y present, baby male
  4. cffDNA first detectable from 4-5 weeks but better around 9
8
Q

Uses of cffDNA?

A
  1. When a sex linked condition is present in the family.
  2. Detects SRY gene (part of Y chromosome)
  3. if male, can go onto further tests
  4. some autosomal dominant single gene disorders that are inherited from father or that rise de novo
9
Q

4 Limitations of NIPT and NIPD

A
  1. Multiple pregnancies - only useful if identical twins
  2. High BMI
  3. Ethical issues
  4. Invasive test may be required
10
Q

5 benefits of NIPT and NIPD

A
  1. Less invasive tests due to sex identification
  2. No risk of miscarriage
  3. Less expertise to perform blood test
  4. NIPT/NIPD can be offered earlier than invasive tests - earlier results
11
Q

Describe invasive prenatal tests.

A
  1. When there is a known risk shown by other prenatal testing, it is offered

These tests are invasive and risks miscarriage

Consists of Chorionic Villus Sampling and Amniocentesis

12
Q

Describe CVS

A
  1. 11-14 weeks
  2. 1%-2% risk of miscarriage
  3. Chorionic villus is part of the developing placenta - so contains foetal DNA
  4. Gives earlier result than amniocentesis (important for abortion)
13
Q

Describe amniocentesis.

A
  1. 16+ weeks
  2. Takes amniotic fluid sample - contains foetal cells
  3. Performed later than CVS
  4. Stick a needle through abdomen
14
Q

Karyotype testing is done is there is a chromosomal abnormality in the family. What other thing may be done?

A

QF-PCR.

ALL PRENATAL SAMPLES HAVE A QF-PCR test.

15
Q

What is a mad reproductive option.

A

Pre-implantation Genetic Diagnosis (PGD)

16
Q

What are the 3 stages of adoption.

A
  1. Registration and checks
  2. Assessment and approval
  3. Search for a child
17
Q

What is pre-implantation genetic diagnosis?

A

Uses IVF but test embryo genetically before implantation.

  1. Ovaries stimulated
  2. Eggs collected
  3. Inseminated - by IVF or ICSI (single sperm injected into each egg)
  4. Fertilisation
  5. Embryo biopsy (when embryo is 8 cells in size, a cell is removed by biopsy)
  6. Embryo testing
  7. Embryo transfer
  8. Pregnancy test
18
Q

What are the eligibility criteria for PGD?

A
  • Female under 40
  • Female BMI between 19 and 30
  • Non smokers (both)
  • No living unaffected children
  • Known risk of being affected by serious condition
  • license from HFEA