Prenatal Screening Flashcards
How many antenatal conditions are screened for?
32
Dating scan?
11-14 weeks
What do you check in dating scan?
- Viability- check heartbeat, (2/3% have miscarried)
- Accurate dating- gauge how many weeks pregnant she is
- Multiple pregnancies (chorionicity)
- Diagnosis of major structural abnormalities (spins bifida, anencephaly)
- Screening for chromosomal abnormalities
Screening for edwards, pataus?
First semester- combined screening
Second semester-quad tests
Edwards is trisomy in?
18
Pataus syndrome is trisomy of ?
13
First semester combined screening?
Maternal age, nuchal translucency scan and blood test for biochemical markers pappa, BhCG
Can choose down and or Patau/Edward
Nuchal traslucency scan can only happen between lengths of?
45-84mm, crown rump length CRL
In normal babies biochemical markers vary?
Free B-hcg is greater and PAPPA is lower
In edwards or Pataus the biochemical markers are?
Lower, lower bhcg and pappa
In downs the biochemical markers are?
Lower bhcg and higher pappa
Maternal factors influencing for combined screening
Maternal age Gestational age Ethnicity Smoking IVF Multiple pregnancy Maternal weight Maternal diabetes Past history of chromosome abnormality Fetal sex Analytical imprecision
What is national cut off for high chance/low chance?
1 in 150
If high chance then result?
Phone within 3 working days offer further tests
Low chance result?
Letter within 2 weeks
Combined test happens when?
11-14 weeks
Quadruple test happens when?
14-20 weeks
Quadruple test only screens for?
Downs
What 4 markers are tested in quads test?
Inhibin a placental hormone
Bhcg
Higher than average
UE3- unconjugated estriol
Alpha fetoprotein
Lower than average
Options after combined/quad screening test?
- Do nothing
- Diagnostic invasive testing - amnio
- Non invasive prenatal testing
Diagnostic invasive testing includes?
Chorionic villus- take tissue of placenta at 11 weeks
Amniocentesis- taking amniotic fluid at 15 weeks
Risk of diagnostic invasive test?
0.5-1% risk of miscarriage, higher in twins
Non invasive prenatal testing includes?
Detecting cell free fetal dna in maternal blood from 10 weeks, 10% from foetus
NIPT offered only up to?
21 weeks and 6 days
Anomaly scan happens at?
18-20 week 6 days
Anomaly scans for how many conditions?
11 Anencephaly Open spina bifida Cleft lip Diaphragmatic hernia Edwards Pataus Lethal skeletal dysplasia Bilateral renal a genesis Exomphalos Gastroschsis Serious cardiac anomalies
How to collect data from anomaly scans?
National congenital anomaly and rare disease registration service ncardrs
Termination of pregnancy with downs in UK?
90%
Grounds e?
Substantial risk if child were born it would suffer from physical and mental abnormalities as to be seriously handicapped
Nuchal fold is from?
Outer edge of occipital bone to skin
UK 1967 Abortion act allows?
Permits abortion at any time if there is a significant risk of baby being born with a serious disability
Support charity for people who are having a downs baby
Antenatal results and choices ARC
When is there a risk of miscarriage?
With diagnostic tests not screening ones
Why is the quadruple test offered?
If pregnancy is too advanced to perform combined test
Unable to measure unchallenged translucency
What is used in quad tests?
Maternal serum screen, and 4 maternal biochemical markers along smoking weight ethnicity gestational age and maternal age
What are the advantages of invasive diagnostic test?
Definitive result
Option for diagnosis by full karyotyping
Monogenic disorders targeted gene panels
NIPT screening for downs?
Sensitivity and specificity is 99%
What is a cousin criteria for NIPT?
maternal cancer [cell free DNA from tumour]
possibility of donor DNA eg after blood transfusion, bone marrow or organ transplant, stem cell therapy
vanished twin pregnancy (second pregnancy sac – either empty or containing non-viable fetus)
known maternal trisomy 21/ balanced translocation/ mosaicism of T13/18/21
Advantages and disadvantages of NIPT?
Advantages
High detection rates, low screen positive rates
Reduction in invasive diagnostic testing [cost effective] hence reduction in miscarriage caused by invasive testing [CVS/amniocentesis]
Disadvantages
Screening test: Not diagnostic [false positives / false negatives]
Confirm high chance results with invasive test
Not suitable for everyone