St A - Prenatal Testing Flashcards
What is prenatal testing?
Consists of prenatal screening and prenatal diagnosis
What is the difference between prenatal screening and prenatal diagnosis?
Screening - focuses on finding problems among a large population with affordable and noninvasive methods.
Diagnosis - Purses additional detailed information once a particular problem has been found, can be more invasive.
What is the purpose of prenatal testing?
- Enable timly medical/surgical treatment before or after birth,
- Give parents time to terminate pregnancy with diagnosed condition,
- Give parents time to prepare psychologically, socially, financially and medically,
- Organise appropriate fetal surveillance
Name some examples of screening methods used in the UK
Blood tests, USS or questionnaires
What is investigates under blood test screening?
- FBC,
- Blood group and rhesus state,
- Haemoglobinopathies (thalasemmia or sickle cell)
- Infectious diseases
- Chromosomal disorders (trisomies 21/18 or 13)
Describe some features of screening for haemoglobinopathies
if women is carrier then partner testing offered, if partner is positive then genetic counselling. Amnuocentesis or CVS to see if fetus is affected and blood spot testing for newborns
Describe features of the first trimester combined test
It uses factors such as maternal age, nuchal translucency measurement, free beta hCG and PAPP-A and gestational age. ideally done from 11-14 weeks of gestation and results show if you are at a low or high chance of having a baby with down’s syndrome
Describe features of second trimester screening
Optimal time is 14-20 weeks. Uses factors of maternal age and biomarkers. It is not as good at detecting downs or edwards’/patau’s syndrome.
If women have a higher chance than 1:150, what are further testing options?
- Non-invasive prenatal testing,
- Chorionic villus sampling or aminocentesis (These are diagnostic tests),
- She can also decide to have no further tests
Describe features of NIPT
- Screening not a diagnostic test which can be preformed from 10 weeks.
- Cell-free DNA material is extracted and analysed from maternal blood test. This can be done as a small amount of the DNA comes from the babys placenta. It has a higher accuracy for finding babies with downs than those with edwards’/patau’s
What is Chorionic Villi Sampling?
Fine needle inserted through abdomen or cervix and into the uterus and a small piece of placenta is removed. It can be used to test for inherited disorders eg, CF, sickle cell, thalassemia and chromosomal disorders. Risks include miscarriage, infection and heavy bleeding.
What is amniocentesis?
Needle inserted through absomen and into amniotic fluid. Used for karyotyping and enzyme assays for inborn errors of metabolism. Done after 15 weeks. Risks are miscarriage, infection and injury
What, when and why is ultrasound screening used?
What - Ultrasound waves so is painless and no risk.
When - 12 weeks for number of pregnancies, viability, Nt thickness, neural tube defects. 20 weeks for anomalys.
Why - Anomaly (physical abnormalities)
What is preimplantation genetic diagnosis (PGD)
It involves removing 1 cell from the early embryo and is offered to parents who are at risk of passing on genetic disorders that could affect capacity for like birth or a gender related disorder. Genetic counselling is offered if a disorder is found
How can you determine how serious a genetic disorder is?
code of pratice gives guidence;
- Consider the views of those seeking treatment,
- Likely degree of suffering,
- Abailability of effective treatment,
- Speed of degeneration,
- Extent of intellectual impairment,
- Family circumstances
