Prenatal screening Flashcards
Purpose of screening
Identifies risk of condition/ disease to allow earlier treatment or informed decisions
Preconception screen
Diabetic
- Diabetic eye test
Sick cell and thalasesemia screening
Screened early
1-10 weeks
Early pregnancy scan
- When
- Things looked for
10-14 weeks
Viability
- Any miscarriage?
- Is the fetus alive?
Accurate dating
- Uses last menstrual period
- Crucial for dating of screening tests
- Avoids inducing labour
Determine chorionicity
- Mono/di
- Monochorionic twins require more monitoring and care
Structural abnormalities
Chromosomal scan
Structural abnormalities in early pregnancy scan
Spina bifida
Anencephaly
Exomphalos
- Weakened abdominal wall
Gastroschisis
- Bowel outside abdominal wall
Bladder flow obstruction.
Most common trisomies
21- Down’s
18- Edward’s
13- Patau’s
Chorionic villus sampling [CVS]
Can be conducted from 11 weeks
- Test material from placenta using a needle
Diagnoses trisomy
Amniocentesis
Conducted from week 16
- Testing of amniotic fluid
1% risk of miscarriage
Combined screening test
- When
- What
11 weeks + 2 days
between
14 weeks + 1 day
Combines three modality
- Maternal age
- Nuchal translucency
- Maternal blood test (PAPPA, beta-hCG)
Maternal age screening
Older age= increased risk of Down’s significantly.
- Egg cells more likely to have extra chromosome due to increased stress
Also
Nuchal translucency scan
Fluid at the back of the neck
- Greater amount of fluid= increased risk of trisomy
Done 11+2 - 14+1 weeks.
Normal
45-84 mm
Free beta-hCG
Tends to be higher than average in Down’s
- Maternal blood tests
- Done in combined test
PAPP-A
Tends to be lower in Down’s
- Maternal blood test done in combined screening
Maternal factors influencing combined screening
Maternal age
Ethnicity
- Affects normal level of biomarkers
Smoking
Weight
- Affects levels in blood
Diabetes
Past history of chromosomal abnormality
Fetal factors influencing combined screening
IVF
- frozen embryo, age is based when the egg was harvested
- Donor egg age considered
Multiple pregnancy
- More than 2 fetus= cannot do accurate screening.
Sex
Combined screening result national cut off
1 in 150
151+ letter in 2 weeks
under 150 or lower= call within 3 days
Combined screening DR and screening positive rate
DR= 82%
SPR= 2.7%
Nuchal translucency
- Description
- Factors screened for
- Further investigations
Fluid in the back of the neck
> 3.5mm = increased risk of:
- Chromosomal anomaly
- Cardiac anomaly
- Sydromes
If increased, further investigations
- Karyotyping
- Fetal cardiac scan
- Anomaly scan
Quadruple test
Second trimester serum screening
- 14+2- 20 weeks
Only assesses Down’s
Looks for levels of
- UE3
- AFP
- Inhibin A
- beta-hCG
Quadruple test detection and positive rate
DR- 75%
SPR- 5.5%
Monochorionic twins
- 80% DR, 3%
Dichorionic twins
- 40-50% DR, 3% SPR
Non-invasive prenatal testing
Cell free fetal DNA
- Placenta sheds fetal DNA
- Can be detected from 10 weeks in maternal blood
- Pregnancy specific
over 99% sensitivity for Down’s
Going to be introduced to women with high chance on combined/ quadruple screening
- Singleton pregnancy
Exclusions of NIPT
Due to risk of false positives
- Maternal malignancy
- Multiple pregnancy
- Blood transfusion within 4 months
- Organ transplant
- Vanished twin
- Known chromosome anomaly
NIPT advantages
High detection rate
Low screen positive rates
Reduction in invasive diagnostics
NIPT disadvantages
Not diagnostic
Screen positive test have to be confirmed with invasive test
