Antenatal Screening - TOG article

Question 1

What happens to the serum markers a-FP, HCG, inhibin A, unconjugated oestriol in trisomy 21?

Answer 1

aFP - very decreased
HCG - raised
inhibin A - raised
uE3 - dereased

Question 2

What happens to the serum markers a-FP, HCG, inhibin A, unconjugated oestriol in trisomy 18?

Answer 2

aFP - decreased
HCG - very decreased
inhibin A - unaffected
uE3 - very decreased

Question 3

What happens to the serum markers a-FP, HCG, inhibin A, unconjugated oestriol in open neural tube defects?

Answer 3

aFP - very raised
HCG - unaffected
inhibin A - unaffected
uE3 - unaffected

Question 4

Where is PAPP-A synthesised and what is its mode of action?

What is the significance of a PAPP-A <0.4-0.5 MoM?

Answer 4

Syncitiotrophoblast

Increases bioavailibiilty of insulin like growth factor
(Protease for IGF binding protein 4)

Associated with adverse fetal outcome - miscarriage, PET, hypertension, LBW, PTD

Question 5

What is b-HCG, where is it synthesised, what gestation does it peak and what is its function?

Answer 5

Glycoprotein (244 amino acids 36kDa)
Syncitiotrophoblast
8-10/40
Stimulates progesterone synthesis by the corpus luteum to maintain pregnancy

Question 6

With which hormones is the a-subunit of the HCG molecule identical?

Answer 6

LH
FSH
TSH

Question 7

What is the significance of low levels of HCG in the first trimester?

Answer 7

Low birthweight

Increased rate of spontaneous miscarriage

Question 8

What is the significance of high levels of HCG in the second trimester?

Answer 8

Large for gestational age placentas
Retroplacental haematomas
Low fetoplacental weight ratio

Question 9

What is aFP, where is it synthesised and when does it peak?

Answer 9

Single polypeptide fetal glycoprotein with 3-5% carbohydrate 69kDa

Fetal yolk sac then by the fetal liver

Peak 13/40

Question 10

Which 2 placental conditions are associated with unexplained maternal serum aFP?

Answer 10

Chorionic vilitis
Vascular lesions of infarction or thrombosis
Adverse obstetric outcomes

Question 11

What is unconjugated estriol (uE3), where is it produced and when does it peak?

Answer 11

Oestrogen hormone

Produced in syncitiotrophoblast from DHEAS (precursor from fetal adrenal gland)

First detected 9/40, plateaus 31-35/40 then rises again from 35-36/40

Question 12

What is the significance of absent or undetectable uE3?

Answer 12

Placental sulphatase deficiency
Smith-Lemli-Opitz syndrome
Anencephaly
Various metabolic disorders
Adverse obstetric outcomes

Question 13

Which serum markers are measured in the combined first trimester screening test?

Answer 13

HCG

PAPP-A

Question 14

Which serum markers are measured in the quadruple second trimester screening test?

Answer 14

AFP
b-HCG
uE3
Inhibin-A

Question 15

Which serum marker is associated with severe pre-eclampsia (but with low sensitivity)?

Answer 15

Elevated inhibin A

Question 16

Which serum marker is associated with abnormal placentation/morbidly adherent placenta?

Answer 16

Raised unexpected maternal serum AFP

Question 17

How does BMI influence serum markers?

Answer 17

Tend to be decreased in raised BMI

Question 18

How does being Afro Caribbean influence serum markers?

Answer 18

Higher levels of AFP, HCG, PAPP-A

Question 19

How does IVF pregnancy influence serum markers?

Answer 19

HCG - Tend to be 10% higher

uE3 and PAPPA tend to be 10% lower

Question 20

How does insulin dependent DM influence serum markers?

Answer 20

Lower levels of AFP and uE3

Question 21

How does smoking influence serum markers?

Answer 21

PAPPA, HCG tend to be 20% lower

Inhibin levels 60% higher