Screening program

Question 1

what is Screening?

Answer 1

a process of identifying apparently healthy people who may be at increased risk of a disease or condition. They can then be offered information, further tests and appropriate treatment to reduce their risk and/or any complications arising from the disease or condition

Question 2

Aims of the The NHS Fetal Anomaly Screening Programme (FASP)

Answer 2

screening to all preg women in England to assess the risk of fetal anomalies. Aims to ensure that there is equal access to uniform and quality-assured screening, and that women are provided with high quality information so they can make an informed choice about their screening options and pregnancy. FASP is overseen by the UK NSC and is part of Public Health England

Question 3

Age related risk of DS at age 20?

Answer 3

1:1450

Question 4

Age related risk of DS at age 49?

Answer 4

1:25

Question 5

FASP defines the national cut off and this is

currently set at

Answer 5

1:150 for both first

and second trimester screening tests.T18,21,,13

Question 6

Prevalence

Answer 6

The number of individuals in a population with the target condition

Question 7

Sensitivity

Answer 7

A screen’s ability to refer individuals (for further tests) who do have the target

Question 8

Specificity

Answer 8

A screen’s ability to NOT to refer individuals who do NOT have the target condition

Question 9

Detection Rate (DR)

Answer 9

The proportion of affected individuals with a positive screening result

Question 10

Screen Positive Rate (SPR)

Answer 10

The proportion of individuals who will be given a high risk result following screening

Question 11

False Positive Rate (FPR)

Answer 11

The proportion of unaffected individuals with a positive screening result. It is the complement of specificity ie: Specificity=100-FPR

Question 12

False negative Rate (FNR)

Answer 12

The proportion of women who are given a lower risk result but have an affected pregnancy. It is the complement to the sensitivity.

Question 13

When is the First trimester combined test conducted?

Answer 13

11+2 and 14+1

Question 14

First trimester combined-what is measured?

Answer 14

maternal age, (NT), free beta hCG and PAPP-A,
+gestational age calculated
from the crown rump length (CRL) = risk of T21 or T18/T13

Question 15

NT of above what is strongly associated with anueploidy?

Answer 15

> 3.5mm

Question 16

in what % of pregnancies of the NT>3.5?

Answer 16

Around 1%

Question 17

What is Serum screening?

Answer 17

Measures levels of serum analytes (markers) that have passed from fetus into mother’s blood

Question 18

Multiples of the Median (MoM) are calculated for each serum marker-what does this represent?

Answer 18

the serum marker concentration for a pregnant woman, divided by the median concentration value for unaffected pregnancies of the same gestational age

Question 19

why is the Multiples of the Median (MoM) used not mean?

Answer 19

not skewed by very high or very low values

Question 20

The national target for the proportion of women with a high risk screening result who are offered a diagnostic test?

Answer 20

97% within 3 working days

Question 21

What can affect serum screen levels?

Answer 21

weight, ethnicity (higher in Afro-Caribbean than in Caucasian), IVF vs non-IVF pregnancies, insulin dependent diabetes mellitus and smoking. Appropriate adjustments of the MoM are made.

Question 22

Second trimester quadruple

test what is measured?

Answer 22

maternal age and four biochemical markers: AFP, hCG (total, intact or free beta subunit), uE3 and Inhibin-A.

Question 23

Date of second trimester quadruple

test?

Answer 23

14+2 to 20+ 0. OPTIMUM 16 weeks

Question 24

When is the foetal anomaly scan performed?

Answer 24

18+0 and 20+6

Question 25

At the foetal anomaly scan which indicators in low risk woman warrant further investigation?

Answer 25

Nuchal fold (>6mm)
Ventriculomegaly (atrium >10mm)
Echogenic bowel (with bowel density equivalent to bone)
Renal pelvic dilation (>7mm)
Small measurements Vs dating scan (<5th centile)

Question 26

When are CVS and AF taken?

Answer 26

CVS from 10 weeks, usually 11 - 14 weeks. 10-25mg

AF from 15 weeks onwards 10-20ml

Question 27

CVS and AF miscarriage rates?

Answer 27

1-2% CVS, 0.5-1% AF.

Question 28

When is foetal blood taken?

Answer 28

18+ weeks. 2-2.5%

Question 29

What is Pregnancy Associated Plasma Protein-A (PAPP-A)?

Answer 29

PAPP-A is a large zinc glycoprotein produced by
the placenta where it is thought to regulate the
activity of factors responsible for the growth of
the placenta. Low levels in maternal blood in the
first trimester are associated with pregnancies
affected by Down’s, Edwards’ and Patau’s
syndromes.

Question 30

What is Free -human Chorionic Gonadotrophin (-hCG)?

Answer 30

hCG glycoprotein produced by the developing embryo and later by the placenta.dimeric molecule composed
-alpha and a beta subunit. The alpha
subunit is common to several other hormones
[luteinising hormone (LH), follicle stimulating
hormone (FSH) and thyroid stimulating hormone
(TSH)]. The beta subunit is unique to hCG.
Concentrations of hCG rise exponentially after
conception reaching a peak at about 9-12
weeks, then falling to reach a plateau at about
20 weeks. Some of the beta subunit (less than
1% of the intact dimeric hCG) is free in the
blood and this molecule can be measured by the
laboratory as a distinct entity. A raised level of
hCG and/or the free beta subunit in the first and
second trimester is associated with an increased
chance of a Down’s syndrome affected
pregnancy. A decreased level is associated with
both Edwards’ and Patau’s syndromes.

Question 31

What is Alpha fetoprotein (AFP)?

Answer 31

AFP is a glycoprotein of 591 amino acids
produced by the yolk sac and the fetal liver. Its
level in fetal serum increases until the end of the
first trimester and then gradually decreases.
Concentrations are much lower in maternal
serum but they continue to rise until about week
32. An increased level in maternal serum is
associated with a possible neural tube defect
such as spina bifida, although ultrasound
scanning is the recommended screening test for
neural tube defects. Decreased levels in the
second trimester are associated with Down’s and
Edwards’ syndromes

Question 32

What is Unconjugated oestriol (uE3)?

Answer 32

Oestriol is one of the three main steroid
hormones produced by the feto-placental unit
during pregnancy. It is made in the placenta
from the 16-hydroxydehydroepiandrosterone
produced by the fetal liver. Once in the maternal circulation most of the oestriol undergoes
conjugation with glucuronides or sulphate but
about 10% remains as the unconjugated form.
Low levels of uE3 in the maternal circulation in
the second trimester are associated with Down’s
and Edwards’ syndromes.

Question 33

What is Inhibin-A?

Answer 33

Inhibin-A is a dimeric molecule comprised of an
alpha and a beta polypeptide chain linked by a
disulphide bridge. (A similar molecule called
Inhibin-B has the same alpha chain but a
different beta chain). It is produced by the
corpus luteum and the placenta during
pregnancy with levels increasing during the first
trimester, then declining to reach a plateau in
the second trimester before increasing again in
the third trimester. Elevated levels in the second
trimester are associated with pregnancies
affected by Down’s syndrome.

Question 34

In the first trimester combined

screen Women can choose to have screening for:

Answer 34

T21 and T18 / T13
T21 only
T18 / T13 only
not to have screening