Mothers who have given birth to children with Down syndrome invariably
ask the question, with tears in their eyes, Doctor, could this not have
been, diagnosed before birth? it could have been, provided the Triple
Marker test and a careful ultrasound had been done.
The opportunity now exists for the obstetrician to prevent the birth of
children with Down syndrome and other chromosomal disorders as well those
with neural tube defects and malformations. This can be done through a
simple blood test during pregnancy - The Triple Marker Test.
We are happy to inform you that at Sir Ganga Ram Hospital we have
perfected the Triple Marker test for the Indian patients to reduce the
burden of malformations and genetic diseases.
The Triple Test Protocol at Sir Ganga Ram Hospital.
This is a non-invasive testing protocol, which improves the ability to
determine the risk of fetal Down syndrome, spina bifida and other anomalies
for pregnant women. Current international practice defines excessive risk as
greater than the numerical risk of fetal Down syndrome for patients at age
35 years (1 : 380 live-born at term), and for spina bifida as risk greater
than 1:150.
Triple Marker test uses ELISA based assays for maternal
serum alpha fetoprotein (AFP), Beta subunit of human chorionic gonadotropin
(b-hcg) and unconjugated estriol (UEst),
combined with patient specific data including age, weight, gestational age,
number of fetuses, and demographics to calculate the numerical risk for
fetal Down syndrome and neural tube defects. It uses a sophisticated
software program called Alpha (developed by Professor Nicholas Waid of UK,
undoubtedly the international leader in this area) to calculate this risk.
A unique feature of this protocol is that median values
for each of these markers at different gestations have been determined
specific to the Indian population, as assayed in our laboratory. This improves
the accuracy, sensitivity and specificity of the test. This is backed by genetic
counselling both before and after the test, and amniocenteses if it becomes
necessary, at an affordable price.
What is the Sensitivity of This Protocol?
Testing these three markers produces test results twice
as sensitive as those obtained from the use of AFP alone. Triple screen will
detect 65% of fetal Down syndrome cases at a risk level of 1:380 (equivalent
to the risk of a 35-year-old patient). The false positive rate is 5% (95%
specificity). If the quadruple test is used the sensitivity of
detection increases to 76%.
Rationale for limiting the sensitivity to 65%.
The sensitivity of the triple screen can be increased to
70 to 80%. However at this level, there is a dramatic increase (10 to 15%)
in false positives, which could lead to unjustifiable doubling or tripling
of amniocentesis procedures.
When to Obtain Serum for Triple Screen?
Serum samples should be obtained in the second trimester
from 15 to 22 weeks of gestation. Out side this gestational age range the
sensitivity and specificity of the test are reduced, while in 1st trimester
different markers are used.
What about Samples Collected in the First Trimester?
For samples collected from
10 to 14 weeks of gestation
different markers are used (PAPP-A, free beta hCG along with ultrasound to
measure nuchal thickness). We have standardised these tests for first
trimester, and can provide their analysis. The values of these two assays,
combined with nuchal thickness as measured on ultrasound has an accuracy of
85% in detecting Down syndrome / other chromosomal disorders in the fetus.
While there is debate over issues involved in choosing between first and
second trimester screening the most effective screening test for Down
syndrome is the integrated test (involving first and second trimester
markers). This has a 94% detection rate for a 5% false positive rate.
How to
Send the Samples?
Three (3) ml of blood in a plain tube should be collected
and sent to us. If samples are being sent from another city use a reliable
courier so that the sample reaches within 48 hours, or get the serum
separated by a local lab. No refrigeration is required. Use vacutainers if
possible, as they do not leak. Keep the tubes in a small plastic box, which
are available from any plastic ware shop.
What is the
Cost of the Test?
The cost of the test including the interpretation by the
Alpha software is Rs. 800 for 2nd trimester screening (excludes genetic
counselling and amniocentesis) and Rs. 1200 for 1st trimester tests.
What Information Should Be Provided Along With the
Samples?
Kindly provide the following information with the sample-
name, date of birth of the woman, date of last menstrual period, weight,
previous history of Down syndrome or neural tube defect, presence of
diabetes mellitus or jaundice, and address where the results is to be sent. If you have a fax
number or email address kindly provide the same.
Turn Around Time For Triple Test
Test results are reported in a maximum of three working
days from receipt of the specimen.
