L18 - Prenatal Screening COPY Flashcards
SCREENING OVERVIEW
i) who does screening identify? what does this allow?
ii) are screening tests diagnostic?
iii) what are the three main screening scans thats take place during pregnancy?
iv) when is a combined test used? when is a quad test used?
i) identifies apparently healthy people who may be at increased risk of a disease and this enables earlier treatment/informed decisions
ii) screening tests are not diagnostic
iii) early pregnancy scan
- screening for downs/edwards/pataus
- foetal anomaly scan
iv) combined test is used for chromo abnorms in the first trimester
- quad test is used for chromo abnorms in the second trimester (if they havent had the combined test)
EARLY PREGNANCY SCAN
i) what are the five aims of this scan?
ii) what time interval is this scan usually given?
iii) what % of women will have miscarried when attending this scan?
iv) give two reasons why accurate dating is important?
v) name four structural abnormalities that can be dx on the early pregnancy scan
vi) name three chromosomal conditions screened for
i) test for viability, accurate dating, detect multiple pregnancy, dx struc abnorms, screen for chromo conditions
ii) between 10-14wks
iii) 2-3% of women will have miscarried
iv) accurate dating is crucial for timing of trisomy tests
- reduces need for induction
v) spina bifida, anencephaly, exomphalos & gastroschisis, bladder outflow obstruction
vi) downs, edwards and patau syndrome
SCREENING FOR CHROMOSOMAL ABNORMALITIES
i) which test is given in the first trimester? which is given in the second trimester?
ii) what trisomy is seen in downs syndrome?
iii) which trisomies are seen in edwards and pataus syndrome?
iv) what do chromo screening tests identify? is there risk of miscarriage?
i) combined screening from 11+2-14+1 weeks (first trimester)
- quad test from 14+2-20wks (second trimester)
ii) trisomy 21
ii) edwards = trisomy 18 and patau = trisomy 13
iv) chromo screening tests identify if the individual has a high or low chance of having a baby with the condition
- no risk of miscarriage
FIRST TRIMESTER COMBINED SCREEN
i) which three things are looked at?
ii) what time point is this offered?
iii) what does it show? (2)
iv) how does maternal age correlate with risk for chromo abnorms? at what age does the risk significantly increase?
i) look at maternal age + nuchal translucency scan + blood markers
ii) between 11+2wks and 14+1wks
iii) gives chance of having trisomy 21 and/or trisomy 13 and 18
iv) increased maternal age = increased risk of chromo abnorms
- risk increases at 36yrs
NUCHAL TRANSLUENCY SCAN
i) where is nuchal fluid found?
ii) what happens to the fluid in conditions such as downs syndrome? what is deemed to be abnormal?
iii) what must the crown rump length be to take the measurement?
i) back of babies neck
ii) in certain conds there can be increased volume of fluid
- >3.5mm is abnormal
iii) must be 45-84mm CRL (equates to 11+2 and 14+1 wks)
MATERNAL SERUM BIOMARKERS
i) which two biomarkers are looked at?
ii) what changes are seen for each one in the case of downs syndrome
iii) which levels of each biomarker are seen in edwards/pataus?
iv) why is this not used as a diagnostic test?
i) free b-HCG and PAPP-A (preg assoc plasma protein)
ii) high BHCG and low PAPPA in downs syndrome
iii) low levels of both marker in edwards and pataus
iv) not diagnostic as there is an overlap between levels in euploid and trisomy populations
MATERNAL INFLUENCING FACTORS FOR COMBINED SCREENING
i) how does maternal age affect risk?
ii) what may be important to consider in IVF?
iii) how many a womans weight influence markers?
i) increased age = increased risk
ii) IVF - consider when the egg was frozen, not how old the woman is
iii) weight = may be taller therefore higher circ blood volume
COMBINED SCREENING RESULTS
i) what is the cut off for a low chance of chromo abnorms from this screening tool?
ii) what is the detection rate for T21 and T13/18?
iii) what risk result is given for monochorionic and dichorionic twins?
iv) whats the screen positive rate for T21 and T13/18?
i) less than 1 in 150 risk
ii) 85% detec for T21 and 80% detec for T13/18
iii) mono = risk for overall pregnancy
di = risk for each individual foetus
iv) screen pos for T21 us 1.8-2.5%
screen pos for T13/18 = 0.1-0.2%
QUADTRUPLE SCREENING TEST
i) what time period can this be given in?
ii) what is the only trisomy that it screens for?
iii) what does it comprise of?
iv) which four maternal markers are looked at?
v) name four other factors that are also incorporated
i) second trimester between 14+2 and 20 wks
ii) only looks for trisomy 21
iii) only a blood test
iv) look at UE3 (made by placenta)
- AFP (made by foetus)
- Inhibin A (placental hormone)
- BHCG (placental hormone)
v) gestational age, maternal age, smoking, weight
QUAD TEST DETECTION RATES AND RESULTS
i) what is the detection rate for trisomy 21?
ii) what is the screen positive rate? what may this lead to?
iii) in which situation may this not be very accurate? why?
iv) what are the three possible next steps if a high chance result is obtained?
i) 80%
ii) screen pos rate is 2.5-3.5% which may lead to more invasive testing and therefore miscarriage
iii) may not be accurate (40-50%) in dichorionic twins as one baby can mask the other
iv) do nothing
- diagnostic invasive testing eg CVS/AC
- Non invasive prenatal testing (NIPT) - currently private
DIAGNOSTIC INVASIVE TESTING
i) what is taken in chorionic villus sampling? in what time frame can this be conducted?
ii) what is taken in amiocentesis? in what time frame can this be conducted?
iii) what is the risk of miscarriage? is this higher or lower in twins?
i) CVS = take piece of the placental
- conducted between 11 and 15 weeks
ii) AC = take amniotic fluid which will contain some of the foetal cells
- can be done from 15 weeks to term
iii) 0.5-1% of miscarriage
- higher in twins
NON INVASIVE PRENATAL TESTING
i) what does it involve and what does it screen for?
ii) at what week will cf foetal DNA be in the maternal blood?
iii) from what week can the test be done?
iv) how specific is screening for T21?
v) who is it exclusively offered to?
vi) name three advatages and three disadvantages
i) involves taking a maternal blood sample and screens for aneuploidy
ii) foetal DNA in maternal blood from 5 weeks
iii) test can be done from 10 weeks
iv) very specific for T21 - 99%
v) only offered to women who have had a high chance result
vi) adv = high detection rate and low screen positive rate
- reduced invasive testing therefore reduce risk of miscarriage
- a further option for women
disadv = screening so not diagnostic
- need an invasive test to confirm result
- not suitable for everyone eg organ transplant or cancer
FOETAL ANOMALY SCAN
i) which time period does this take place?
ii) how many conditions does it screen for? which three situations may arise due to the baby having the condition?
iii) name the conditions screened for
iv) which registry collects data on babies born with these conditions?
i) from 18 ti 20+6 weeks
ii) screens for 11 conditions
- baby may benefit from treatment antenatally
- birth is advised at a specialist centre
- baby may die shortly after birth
iii) ananecephaly, open spina bifida, cleft lip, diaphragmatic hernia, gastrochisis, exomphalos, cardiac abnorms, renal agenesis, edwards/pataus, lethal skeletal dysplasia
iv) national congential anomaly and rare disease reg service (NCARDRS)
WHAT IF A CONDITION IS DIAGNOSED?
i) what two things is it important to ask/communicate?
ii) what are the three options for the mother?
iii) under what ground of the abortion act is termination allowed? what condition must be met?
iv) name three other professionals that can provide additional support
i) what is the parents understanding and balanced info about the condition (ie T21 can still live a nice life)
ii) continue, adoption, termination
iii) grounds E of abortion act if child may suffer from phys/mental abnorms
iv) antenatal screening midwife, national support groups, clinicians, genetic counselling
