Prenatal screen

Question 1

Available first trimester investigations

Answer 1

Combined test
Quad test
USS
NIPT
Invasive - CVS

Question 2

Elements and timing of combined test

Answer 2

11-14/40
If NT >35mm
HCG, PAPP-A
Features of T21 - inc HCG, dec PAPP-A

Question 3

Elements, timing and interpretation of Quad test

Answer 3

14-20/40
AFP, Estriol, hCG, Inhibin A
(A E H I)

T21: HI - inc HCG, Inhibin, low AFP, estriol
XO: HI - inc HCG, inhibin, low AFP, estriol
T18: HE is low - low HCG and estriol
T13: AFPatau high - elevated AFP

AFP also elevated in spina bifida and abdo wall defects

Question 4

Ultrasound features T21:

Answer 4

30% ASD/ VSF, duodenal atresia, omphalocoele, ventriculomegaly, cystic hygroma

Question 5

Soft markers in ultrasound

Answer 5

Present in 5% pregnancy
include:
choroid plexus cyst, mild renal pelvis dilatation, echogenic bowel, echogenic cardiac foci, mild cerebral ventricular abnormality
If multiple present, higher risk of chromosomal abnormality

Question 6

Role and timing of NIPT

Answer 6

9-11/40
Screens cell-free DNA
Detection rate:
T21 99%, X0 96%, T18 98%, T13 80%

Question 7

Possible sources of error in NIPT

Answer 7

Twins
Maternal BMI
Vanishing twin
Early gestational age
Placenta/ maternal mosaicism

Question 8

Invasive prenatal testing types and timings

Answer 8

CVS vs amnio
CVS >10/40, transcervical 11-13/40, transabdominal >12/40
Amnio: >15/40, takes 1-20ml
PCR tests for specific abnormalities, full karyotypes

Amnio can do FISH or PCR

Question 9

Risks of invasive prenatal testing

Answer 9

Chorioamnionitis
Haematoma
Haemorrhage
Rh sensitisation
Fetal infection/ injury
Miscarriage
- amnio: 1% risk
- CVS: 1-2% risk