Prenatal diagnosis and genetic screening Flashcards
What occurs during a normal pregnancy?
- Positive pregnancy test
- Booked into antenatal care - see midwife
- Nuchal scan (ultrasound) 10-14 weeks
- Nuchal translucency (12 week scan)
another scan 20-22 weeks
What is the function of a nuchal translucency?
- measure fluid in back of baby neck - ca 3.5mm
- Increase can indicate: Chr abnomaltities - specifically Down’s risk
- Birth defects e.g cardiac, pulmonary, renal, abdominal abnormalities
- Early miscarriage
What are indications for further genetic testing?
- Following abnormal nuchal/mid trimester scan
- Results of combined tests at inc risk
- Previous affected pregnancy
- Family history
- Parents is carrier
What are the aims of prenatal testing?
- Inform and prepare parents
- Offer in utero treatment
- Helps manage rest of pregnancy - extra scans and blood tests
- Allow parents to prepare for post birth complications
What are the types of non invasive tests?
MRI: older than 20 weeks
Ultrasound:
- NT and nasal bone: soft marker - presence/absence
indicates DS
- High level/anomaly scan - detailed images
- Early dating scan - confirming pregnancy
- Foetal cardiac scan indicates heart problems
What are limitations of non invasive tests?
indication but not accurate diagnosis
What are the types of minimally invasive tests?
- Blood screening
- Maternal serum screening
○ serum markers in blood detect trisomy 112 and 18 and/or neural tube defects - Cell free fotal DNA (cffDNA) - particualry when chance of x linked condition
○ Determines sex
○ Small amount of DNA in blood can be isolated to look for Y Chr
○ Most accurate 9 weeks an older
○ Cff cleared form blood and hour after birth
○ Males undergo further tesitng not needed for females
What are the limitations of minimally invasive tests?
- Multiple pregnancies: don’t know which DNA
- High BMI reduced ratio of baby: mum DNA
- Ethical issue: implicaton of results
- Invasive tests may still beneeded
What are the benefits of minimally invasive tests?
- No risk of miscarriage
- No invasive test
- Less expensive
- Offered earlier than invasive
When are invasive tests offered?
when known risk
What are the types of invasive tests?
CVS: 11-14w, 1-2% chance of miscarriage
- Transabdominal or vaginal - Villus part of placenta and have smae baby dann - Earlier reuslts than amniocentitis - Important for parents deciing on termination
Amniocentitis: 16w, 1% miscarriage risk
- Later results - Needle through abdomen
What are some alternative reproductive options?
- Conceive naturally
- Egg/sperm donor - children have right to contact donor when 18
- Via licensed feritility center conforming to strict ethical, medical and legal standards - Adoption done in 2 stages
- Registrations and checks
- Assessment and approval - Pre-Implantation genetic diagnosis
How does PIGD work?
- Stimulate overy egg production
- Collect eggs
- Inseminate via IVF of intra cytoplasmic sperm injection
- Fertilisation
- Embryo biopsy (1/8 cells removed)
- Embryo testing
- Embryo transfer (max 2)
- Pregnancy test
What is the eligibility criteria of PIGD?
- Under 40
- BMI 19-30
- Both non smoker
- No living unaffected child
- Known risk
- In stable relationship
- License each condition (usually 3 round are funded if eligible)
- Hormone levels must suggest would respond to treatment
- No welfare concerns for unborn child
What are the problems with PIGD?
- Lengthy
- 30%success rate per cycle
- 40% success rate for transfer
- Mental and physical implication
- Offered privatelyl, costs 13,000 pounds
When is PIGD used?
- Huntignton’s
- CF
- translocation carrier
- Duchenne muscular dystrophy
- BRCA 1/2
How does one discuss genetic counselling?
- Arrange and explain tests
- Fascilitiate decision making
- Give reuslts
- See patient following in utero diagnosis
- Arrange termination
- Discuss recurrence risks and future plans
What does one have to consider?
- previous experience
- Family situation
- Religion
- Personal beliefs
- Psychosocial situation
- Risk of miscarriage vs. Genetic
- Couples don’t always agree
- access to support
