Prenatal diagnosis Flashcards
What are the benefits of prenatal screening
Parental reassurance of normal
If abnormality is detected the increased options eg. further testing, referral, counselling.
Altered obstetric management
Facilitated neonatal management
What are the risks of prenatal screening
Parental anxiety
False positives
Pregnancy complications
Pregnancy loss
What are the current methods for screening for chromosomal abnormalities
Integrated prenatal screening
First trimester combined screeening
Quadruple maternal serum screening
What is integrated prenatal screening
Nuchal translucency PAPP-A hCg AFP (alpha fetoprotein) uE3 inhibin A
What is first trimester combined screening
Nuchal translucence, hCG, PAPP-A
What is quadruple maternal serum screening
hCG, AFP, uE3, inhibin A
What is nuchal translucency
Fluid-filled space between back of fetal neck and skin
Measured between 11-13 +6/7
Increases with gestational age
>3-3.5mm cosidered elevated
What happens if nuchal translucency is elevated
Diagnostic testing
Fetal echocardiogram around 20 weeks
Detailed anatomy scan 18-20 weeks
Genetic counselling
What is elevated nuchal translucency indicative of
Trisomies 21, 18, 13, Turner syndrome
spontaneous fetal loss
Cardiac defects, diaphragmatic hernia, pulmonary defects, skeletal dysplasia, congenital infection
Chance on normal birth decreases with increased size
What are the non-invasive methods of chromosomal evaluation
Fetal cells from maternal blood
Preimplantation embryos
What are the invasive methods of chromosomal evaluation
Amniocentesis
Chorionic villus sample
Fetal blood
What can testing evaluate
Chromosomal aberrations- trisomy, monosomy, polyploidy, marker chromosome, deletion, duplication, inversion, translocation
Genetic aberrations
Infectious disease
Biochemical markers
What is amniocentesis
Sample of amniotic fluid Percutaneous 20g needle 20cc amniotic fluid Results in 2-3 weeks
What are the complications of amniocentesis
1% pregnancy loss Increased risk if needle larger than 18g, multiple needle insertion, discoloration of fluid, high AFP, multiple late miscarriages, previous vaginal bleeding, placental perforation Leakage of amniotic fluid amnionitis Vaginal bleeding Needle puncture of fetus
What are the potential long term complications of amniocentesis
Respiratory distress
Isoimmunisation
How is HIV related to amniocentesis
Increased rates of vertical transmission
Chemoprophylaxis before amniocentesis can prevent
What is chorionic villus sampling
Direct analysis- trophoblast cells of placenta. Results in hours but vulnerable to mitotic error
Cultured analysis- fibroblast like cells of villus stroma. results in 10-14 days, more accurate
What is true chromosomal mosaicism
2 or more abnormal cell lines detected in 2 or more cultures from the same individual
What is pseudomosaicism
2 abnormal cell lines found in only 1 culture
What is the detection rate of mosaicism
1-2% in CVS
0.1% in amniocentesis
What is the clinical outcome of mosaicism
Strongly dependent of specific chromosome involved + number of trisomic cells in placenta + fetus
What are the 4 possible conditions if trisomy mosaicism is detected in CVS
- Mosaicism only in placenta, not affecting fetus or placental function
- Mosaicism only in placenta, affecting placental function (IUGR) but not fetus
- Trisomic cells in both placenta and fetus
- Trisomic cells in placenta, uniparental disomy in fetus
What happens if mosaicism is detected at amniocentesis
Trisomic cells are probably present in fetus but true level and distribution cannot be accurately assessed with any prenatal procedure so ultrasound used
What is uniparental disomy
Individual inherits 2 copies of a chromosome pair from one parent and no copy from the other parent
