What is the purpose of the nuchal scan that occurs 10-14 weeks into pregnancy?
Date pregnancy, check if twins, check babies development, etc
Assess risk of chromosomal abnormalities
Nuchal scan done by looking at nuchal translucency.
What is nuchal translucency (NT)
Used in conjunction with maternal age to detect Downies
Measures fluid at the back of the babies neck,
Increased NT (>3mm) could indicate:
- Chromosomal abnormalities
- Birth defects
- Skeletal dysplasia
When is prenatal testing arranged?
- 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
What are the 3 types of prenatal tests?
- Non invasive (ultrasound)
- Minimally invasive (maternal blood test/cell free foetal DNA)
- Invasive (amniocentesis/Chorionic Villus Sampling)
Describe Non invasive prenatal tests.
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
Describe a Minimally Invasive Prenatal test
-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.
- 2nd Trimester - 16-20 weeks, looks for HCG/PAPP A/AFP/uE3 (oestriol)
- Nuchal Translucency Measurement - 11-14 weeks
IF FOUND THAT WOMAN AT RISK OF GENETIC DISEASE, INVASIVE PROCEDURES OFFERED
What is cell-free Foetal DNA test (cffDNA)?
OFFERED ESPECIALLY IF BABY HAS RISK OF HAVING AN X LINKED CONDITION
- Test done to determine sex of baby
- Some foetal DNA is present in maternal blood
- Blood test done which isolates baby DNA and looks for Y chromosome
- If Y present, baby male
- cffDNA first detectable from 4-5 weeks but better around 9
Uses of cffDNA?
- When a sex linked condition is present in the family.
- Detects SRY gene (part of Y chromosome)
- if male, can go onto further tests
- some autosomal dominant single gene disorders that are inherited from father or that rise de novo
4 Limitations of NIPT and NIPD
- Multiple pregnancies - only useful if identical twins
- High BMI
- Ethical issues
- Invasive test may be required
5 benefits of NIPT and NIPD
- Less invasive tests due to sex identification
- No risk of miscarriage
- Less expertise to perform blood test
- NIPT/NIPD can be offered earlier than invasive tests - earlier results
Describe invasive prenatal tests.
- 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
Describe CVS
- 11-14 weeks
- 1%-2% risk of miscarriage
- Chorionic villus is part of the developing placenta - so contains foetal DNA
- Gives earlier result than amniocentesis (important for abortion)
Describe amniocentesis.
- 16+ weeks
- Takes amniotic fluid sample - contains foetal cells
- Performed later than CVS
- Stick a needle through abdomen
Karyotype testing is done is there is a chromosomal abnormality in the family. What other thing may be done?
QF-PCR.
ALL PRENATAL SAMPLES HAVE A QF-PCR test.
What is a mad reproductive option.
Pre-implantation Genetic Diagnosis (PGD)
What are the 3 stages of adoption.
- Registration and checks
- Assessment and approval
- Search for a child
What is pre-implantation genetic diagnosis?
Uses IVF but test embryo genetically before implantation.
- Ovaries stimulated
- Eggs collected
- Inseminated - by IVF or ICSI (single sperm injected into each egg)
- Fertilisation
- Embryo biopsy (when embryo is 8 cells in size, a cell is removed by biopsy)
- Embryo testing
- Embryo transfer
- Pregnancy test
What are the eligibility criteria for PGD?
- 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