Prenatal screening Flashcards
NHS fetal anomaly screening
Early pregnancy scan
Screening for Down’s Edward’s Patau’s syndromes
- first trimester combined test
- second trimester quad test
18+0 - 20+6 fetal anomaly scan
Why scan at 10-14 weeks?
Viability
Accurate dating
Detect multiple pregnancy
Diagnosis of structural abnormality
Screening for chromosomal conditions
Structural abnormality
Spina bifida
Anencephaly
Exomphalos and gastroschisis
Bladder outflow obstruction
Chromosomal conditions
Down’s- trisomy 21
Edward’s- trisomy 18
Patau’s- trisomy 13
Prenatal diagnosis/ diagnostic invase test
Chorionic villus sampling CVS 11+ weeks
Amniocentesis 16+ weeks
Around 1% risk of miscarriage
Maternal/ fetal influencing factors for combined screening
Maternal age
Gestational age
Ethnicity
Smoking
IVF
Multiple pregnancy
Weight
Diabetes
Past history of chromosome abnormality
Fetal sex
Analytic impression
Increased NT > 3.5mm
Increased change of
- chromosomal anomaly
- cardiac anomaly
- syndromes
Quadruple test
14+2 to 20 weeks: late booker only
Chance of T21
Gestational age, maternal age, smoking, weight, ethnicity
Non-invasive prenatal testing
Cell free fetal DNA in maternal blood from 5 weeks
Pregnancy specific
Test maternal blood from 10 weeks
Aneuploidy: screening for T21 sensitivity and specifically over 99%
Absolute exclusions of NIPT on the NHS
Risk of false positive results
- maternal malignancy
- multiple pregnancy
- blood transfusion within 4 months
- organ transplant
- vanished twin/ demised twin
- known chromosome or genetic anomaly in mother
Advantages of NIPT
High detection rates, low screen positive rates
Reduction in invasive diagnostic testing
A further option for women
Disadvantages of NIPT
Screening test: not diagnostic
Confirm screen positive results with invasive test
