Prenatal Screening & fetal abnormalities Flashcards
1
Q
What is screening?
A
- screening identifies apparently healthy people who may be at increased risk of a disease or condition, enabling earlier treatment or informed decisions
2
Q
What are the main screening tests?
A
- Early pregnancy scan
- Screening for Down’s Edward’s Patau’s syndrome
- first trimester combined test
- second trimester quad test
- 18+0 - 20+6 fetal anomaly scan
3
Q
What is the purpose of the early pregnancy scan?
A
- checks for viability
- 2-3% of women attending for the scan will have miscarried
- Accurate dating
- NICE guidance: advise using a scan of dates in lieu of LMP dates
- crucial dor screening tests for trisomies
- reduces the need for postdates induction of labour
- Detect multiple pregnancies
- determines chorionicity
- Diagnosis of major structural anomalies
- spina bifida
- anencephaly
- exomphalos & gastroschisis
- bladder outflow obstruction
- Screening for chromosomal conditions
- Down’s Syndrome - Trisomy 21
- Edward’s syndrome - Trisomy 18
- Patau’s syndrome- Trisomy 13
4
Q
What is the difference between a screening test and a diagnostic test?
A
- Screening test: identifies individuals at high or _low-_risk chance of having a baby with a conditioned screened for
- there is no risk of miscarriage in these tests
- Diagnostic test: give definitive information on the fetal chromosomes by confirming the presence of an extra chromosome or absence of one
- there is a risk of miscarriage in these tests
5
Q
Go through the pregnancy screening timeline
A
- Screening for T21, T18, T13
- combined test 11+2 to 14+1 wks
- Quadruple test 14+2 to10wks
- Screening for fetal anomaly
- anomaly scan 18-20+6wks
- Diagnostic tests
- CVS at 11+0 to 15wks
- Amniocentesis from 15 wks
- blood tests for screening should be booked by 10 wks
6
Q
What is carried out as part of the First trimester combined screening?
- what does it assess?
A
- Maternal age
- Nuchal Translucency Scan
- this is the thickness of the nuchal fluid behind the fetal neck
- the CRL (crown-rump length), can also be measured to help with dating
- Blood test for markers
- PAPP-A (pregnancy-associated plasma protein)
- low around 0.5 MoM
- Beta-hCG
- high around 2.0 MoM
- PAPP-A (pregnancy-associated plasma protein)
- this screens for chromosomal abnormalities
- has a sensitivity of 90% if the detection of T21
7
Q
What does a CRL of 45-84mm indicate?
- what is it?
A
- CRL is crown-rump length, this can be measured in a nuchal translucency (NT) scan
- and it equates to 11+2 to 14+1 weeks old fetus
8
Q
What are Maternal/ fetal influencing factors that indicate combined screening?
A
- Maternal age
- gestational age
- ethnicity
- smoking
- IVF
- Multiple pregnancies
- weight
- diabetes
- past history of chromosome abnormality
- fetal sex
- analytical imprecision
9
Q
What is carried out during the second-trimester maternal serum screening: quadruple test?
A
- only screens for T21 and is only offered to those who couldn’t do an early scan
- only blood tests are done as an NT cannot be done after 14+2 weeks
- use maternal/fetal influencing factors and maternal serum markers to give a diagnosis
- Maternal serum markers include:
lower than expected
- UE3 unconjugated estriol -the placental hormone
- AFP alpha-fetoprotein
higher than expected
- Inhibin A placental hormone
- BHCG (beta-human chorionic gonadotropin)
10
Q
What options are available if the combined or quadruple test indicates a higher chance of T13/18/21?
A
- do nothing- continue pregnancy without having further tests
- Diagnostic invasive testing (miscarriage risk)
- CVS: Chorionic Villus sampling 11+ wks
- Amniocentesis 15+ weeks to term
- Non-invasive prenatal testing (NIPT)
- available privately, planned implementation on the NHS in June 2021
- cell free fetal DNA (maternal blood from 5 weeks)
- the options should be explained to them, and a discussion about what a potential diagnosis and further testing would mean for the parent(s)
11
Q
What are the advantages of a Non-Invasive Prenatal screening Test?
A
- High detection rates, low screen positive rates
- Reduction in invasive diagnostic testing [cost effective] hence reduction in miscarriage caused by invasive testing [CVS/amniocentesis]
- A further option for women
12
Q
What are the disadvantages of a Non-Invasive Prenatal screening Test?
A
- Screening test: Not diagnostic [false positives / false negatives]
- Confirm screen positive results with an invasive test
- Not suitable for everyone, accuracy is reduced in
- multiple pregnancy
- obesity
- women at < 10wks gestation
13
Q
What is the use of ultrasound scanning reform 18+0 to 20+6 weeks?
A
- There are a main 11 conditions which are screened for at the mid-trimester scan
- the baby may benefit from treatment before or after birth
- birth is advisable in an appropriate hospital/ centre and/or to optimise treatment after the baby is born
- the baby may die shortly after birth
14
Q
What 11 conditions are screened fore at the mid-trimester scan?
A
- Ancencephaly
- Open spina bifida
- Cleft lip
- Diaphragmatic hernia
- Gastroschisis
- Exomphalos
- Serious cardiac anomalies
- Bilaterla renal agenesis
- Lathal skelatal dysplasia
- Edwards’ syndrome T18
- Pataus’s syndrome T13
15
Q
What serious cardiac anomalies are screened for at the mid-trimester scan?
A
- Transposition of the Gret arteries
- Atrioventricular Septal Defect
- Tetralogy of Fallot
- Hypoplastic Left Heart Syndrome
