|
Multi-marker screening
tests
Genmark™
Combines 4 blood markers at 14-20
weeks and two ultrasound markers.
Addmark®
Combines 4 blood markers and 2 ultrasound markers at 9-13
weeks If risk is borderline, 4 further markers tested after
14 weeks gestation and risk revised.
Tipmark
Our new test which does not involve a blood sample being
taken by a professional. Instead, a finger-tip kit is
provided so blood drops can be obtained at home. Two blood
markers plus ultrasound substantially improves accuracy
compared with ultrasound alone.
Risk
Accuracy
Using our additional
markers, more pregnancies with Down's syndrome are shown to
have a high risk (i.e. 'detected) and overall fewer
pregnancies are given a risk which is high (i.e.
'positive').
|
Overall |
|
Test |
Week |
Detected*
|
Positive |
|
Genmark™ |
9-13 |
91% |
1.2% |
|
|
14-18 |
80% |
2.7% |
|
Addmark® |
9-13 |
93% |
0.6% |
|
Tipmark |
9-13 |
90% |
1.3% |
|
*Also, Edwards' syndrome about 90% if
9-13 weeks; spina bifida about 75% if 15-20 weeks.
|
|
|
Without NB or NBL* |
|
Test |
Week
|
Detected
|
Positive |
|
Genmark™ |
9-13 |
84% |
1.8% |
|
|
14-18 |
76% |
3.0% |
|
Addmark® |
9-13 |
89% |
1.1% |
|
Tipmark |
9-13 |
84% |
1.9% |
|
*Some
scan centres do not determine nasal bone and occasionally the fetal
position obscures it. Detection is lower in these circumstances. |
Maternal
Age
The above table gives overall rates for UK women. Because
the risk of Down's syndrome increases with maternal age, the
percentage of Down's syndrome pregnancies with high risk and
the percentage of pregnancies with high risk also
increases.
|
|
|
Age 25 |
|
Age 30 |
|
Test |
Week |
Detected |
Positive |
|
Detected |
Positive |
|
Genmark™ |
9-13 |
87% |
0.8% |
|
89% |
1.1% |
|
|
14-18 |
70% |
1.5% |
|
74% |
2.3% |
|
Addmark® |
9-13 |
92% |
0.4% |
|
92% |
0.6% |
|
Tipmark |
9-13 |
87% |
0.8% |
|
89% |
1.2% |
|
|
|
Age 35 |
|
Age 40 |
|
Test |
Week |
Detected |
Positive |
|
Detected |
Positive |
|
Genmark™ |
9-13 |
92% |
2.2% |
|
95% |
5.9% |
|
|
14-18 |
82% |
5.4% |
|
91% |
16% |
|
Addmark® |
9-13 |
93% |
1.1% |
|
94% |
2.0% |
|
Tipmark |
9-13 |
92% |
2.3% |
|
95% |
6.4% |
Twins
The above tables give the test accuracy for women who do not
have twins. The accuracy in twins depends on whether they
are identical or not which can be determined by examination
of the sacs and membranes. In identical twins the accuracy
of Tipmark, Genmark™ and Addmark® is similar to that in
non-twins, but when the twins are not identical accuracy is
lower.
|
Test |
Week |
Detected |
Positive |
|
Genmark™ |
9-13 |
87% |
1.4% |
|
|
14-18 |
66% |
2.8% |
|
Addmark® |
9-13 |
89% |
1.9% |
|
Tipmark |
9-13 |
88% |
1.6% |
Test Interpretation
If a blood sample is taken a week earlier, a result will be
given immediately after the ultrasound scan. If the sample
is taken at the time of the scan, a result will be given 3-5
working days later by telephone and in writing. The result
will include the actual risk of Down's syndrome as a risk of
1 in …as well as the interpretation as 'Screen Positive'
meaning high risk and 'Screen Negative' meaning lower risk. |
