L13 - Prenatal Screening

Question 1

when are scans done?

what tests are they and for what

Answer 1

Early pregnancy scan

Screening for Down’s Edward’s Patau’s syndromes

First trimester combined test
Second trimester quad test

18+0 — 20+6 weeks fetal anomaly scan

Question 2

why scan at 10-14 weeks?

Answer 2

VIABILITY
2-3% have miscarried

ACCURATE DATING

DETECT MULTIPLE PREGNANCY
—determine chorionicity

DIAGNOSIS OF STRUCTURAL ABNORMALITY

• • spina bifida
• • anencephaly
• • exomphalos & gastroschisis
• • bladder outflow obstruction

SCREENING FOR CHROMOSOMAL CONDITIONS
downs -trisomy 21
Edwards 18
patau’s 13

Question 3

prenatal diagnosis / diagnostic invasive test

what is it
when is it done
what is the risk of it

Answer 3

chorionic villus sampling CVS 11+ weeks
amniocentesis 16+ weeks

1% miscarriage risk, higher in twins

Question 4

what is the difference between screening test and diagnostic tests

Answer 4

Screening Tests… .
.identify individuals at ‘high’ or ‘low’ chance of having a baby with a trisomy
A low chance result does not exclude trisomy in the baby.
A high chance result does not indicate that the baby is definitely affected.
No risk of miscarriage

Diagnostic Tests…
-give definitive information on the fetal chromosomes by confirming the presence of an extra chromosome or absence of a chromosome
Risk of miscarriage

Question 5

what is the first trimester combined screening

Answer 5

maternal age
scan
and PAPPA BhCG

together can be used to see the chance of a baby having trisomy 21/18/13

Question 6

how does maternal age vary with chr abnormality risk

Answer 6

incr for everything (trisomy 21,18.13

stays the same for turners and triploidy

Question 7

NT scan

what is it and what does it imply the risk of

Answer 7

Nuchal translucency scan
it is incr in over 80% of T21 cases,
and 75 of T18 and 87 of Turners

Question 8

in combined screening, what maternal serum biomarkers can you look out for T21?

Answer 8

T21 has higher free B-hCG (beta)
T21 has lower PAPP-A

• –in maternal serum
• -compared to euploid

Question 9

what maternal and fetal influencing factors would you think about when screening? (combined scr

Answer 9

Maternal age 
Gestational age 
Ethnicity 
Smoking 
Multiple pregnancy 
Weight 
Diabetes 
Past history of chromosome abnormality 
Fetal sex 
Analytical Imprecision

Question 10

results for combined screening:

what is the cut off for a high?
how quick would you contact

detection rate?
screen positive rate?

Answer 10

1 in 150
higher chance
— 3 working days phone
lower - 2 weeks letter

82%
2.7%

Question 11

what happens if you have an increased NT?
above what value are you concerned

what doe sit increase chances of and what would you offer them

Answer 11

INCR chance of chromosomal anomaly
cardiac anomaly
syndromes

offer
karyotyping – array CGH
fetal cardiac scan
anomaly scan

Question 12

QUADRUPLE TEST
what is it
when do you do it
what are you looking for

what maternal serum markers do you look for

Answer 12

second trimester maternal serum screening: quadruple test

14+2 to 20 weeks: late bookers only

only checking for T21 chance

DECR UE3 and AFP
incr inhibin A an BHCG

Question 13

quadruple test

what are the detection rates like

Answer 13

Quad test : Detection rates dichorionic twins have half the detection rate of monochorionic twins – 40-50%

Question 14

what do you do once a higher chance of T21/18/13 has been found?

what options do you give

Answer 14

1. do nothing
2. diagnostic invasive testing (CVS / amnio)
3. NIPT non invasive prenatal testing
   - – not available on NHS atm

Question 15

NIPT what is it

what are you looking for

Answer 15

cell free fetal DNA – cff DNA in maternal blood from 5 weeks
preg sp
test maternal blood from 10 weeks
aneuploidy: screening for T21 sensitivity and specificity over 99%

marketed as harmony, SAFE, panorama, NIFTY test

Question 16

in terms of results how do combined screening and NIPT differ

how would it be offered on NHS?

what are the exceptions of this?

what are the advantages and disadvantages of having NIPT on NHS

Answer 16

NIPT you either have 1:1 chance of getting it or 1:10,000

combined its a lot more varied and relies on other factors such as crown rump length

NIPT leads to a lot less invasive procedures

offered on NHS to women with high chance result on screening with a SINGLEton pregnancy

absolute exceptions –
maternal malignancy, multiple preg, recent 4 month blood transfusion, organ transplant, vanished twin / demised twin, known chromosome or genetic anomaly in the mother

ADVANT
high detection rates, low screen positive rates, reduction in diagnostic testing (cost effective), further option for women
DISADVANTAGES
screenin test - not diagnostic – false positives / negatives
confirm screen positive results with invasive tests

Question 17

once a condition is diagnosed, what are the options and what is the support available?

Answer 17

Options

• Continue
• Continue and adoption
• Termination [medical / surgical]

Support
— Antenatal Screening Co-ordinator
— National support groups: [Trisomy 21: 90%]
Antenatal Results and Choices [ARC]
Downs syndrome association [DSA]
Soft U.K. [Tri 13 and 18], Unique, Contact-A- Family
— Meet other parents [Specialist Health Visitor / local groups]
— Obstetric/ neonatal / paediatric teams
— Genetic counselling