Antenatal screening

Question 1

Anaemia

Answer 1

FBC at booking + 28w

If Hb <11 = Dietary advice Fe + folate) + Fe supplement + Folate supplement (400ug up to 12w at least)

Question 2

GDM

Answer 2

OGTT at booking + 24-28w if previous GDM, at 24-48w if RFs, at 28w for all
If >7.8mmol/L - GDM

Question 3

Red cell autoantibodies

Answer 3

G+S at booking + 28w + after sensitising events

Question 4

Haemoglobinopathy

Answer 4

Hb electrophoresis at booking

Question 5

NTDs

Answer 5

Dating / anomaly scan

Question 6

Hepatitis B / HIV / Rubella / Syphilis

Answer 6

Serology at booking

Question 7

What screening tests are done at booking?

Answer 7

FBC
G+S (ABO, RhD)
Hb electrophoresis
Infection screen (Rubella, Syphilis, HIV, HepB)
MSU
BP, protein in urine
OGTT if risk factors for GDM

Question 8

What infections are tested for at booking?

Answer 8

Rubella
Syphilis
HepB
HIV

Question 9

Combined screening test

Answer 9

<14w
NT + PAPP-A + B-hCG
(+ maternal factors - age, weight, ethnicity)

Question 10

Quadruple screening test

Answer 10

> 14w
B-hCG + AFP + inhibin-A + uE3
(+ maternal factors - age, weight, ethnicity)

Question 11

What does the combined screening test screen for that the quadruple does not?

Answer 11

Edward’s (T18) and Patau’s (T13)
Cannot use nuchal translucency
It is less accurate + measures for less things

Question 12

If a baby has Down’s syndrome, what happens to each of the parameters?

Answer 12

Things with ‘b’ in increase
B-hCG and inhibin-A increase
PAPP-A, AFP and uE3 decrease

Question 13

What is classified as ‘high-risk’ and requiring diagnostic invasive testing?

Answer 13

> 1 in 150

AND mother must agree

Question 14

What effect does maternal age have upon risk of Down’s syndrome?

Answer 14

20y - 1 in 1500
30y - 1 in 800
35y - 1 in 270
40y - 1 in 100
45y - 1 in 50

Question 15

What are the two types of invasive prenatal test and when can they be conducted?

Answer 15

Chorionic villous sampling (11-13+6) - sample of placental villi containing trophoblast cells
Amniocentesis (15w and over) - 15-20ml sample of amniotic fluid containing amniocytes + fibroblasts from fetus
(CBA - C before A)

Question 16

What happens in both CVS and amnio?

Answer 16

• USS scan beforehand to check gestation, viability, fetal position + placental position
• Anti-D if RhD-
• Small risk of infection in both (1 in 1000)
• Spotting + cramping for a few hours after (paracetamol)
• Safety net for unusual symptoms (shivering, fluid loss, bleeding, contractions)
• Appt. after to discuss results + make decision

Question 17

What is sampled in CVS?

Answer 17

Trophoblast cells from placenta

Question 18

What is sampled in amnio?

Answer 18

Fibroblasts and amniocytes shed from fetus in amniotic fluid

Question 19

Why can CVS not take place <11w?

Answer 19

Uterus is to small and placenta is too thin - difficult to obtain sample!

Question 20

What approach can be used for CVS / amnio?

Answer 20

CVS - TV or TA
Amnio - TA only

(earlier = more flexible)

Question 21

What are the risks associated with CVS?

Answer 21

Slightly higher risk of miscarriage (1-2%) as earlier

Placental mosaicism in 1% of samples - will require amnio

Question 22

What are the risks associated with amnio?

Answer 22

Lower risk of miscarriage as later (1%)
<15w higher fetal loss, fetal talipes, resp morbidity
<7% needs repeating as insufficient fluid sampled