Juniper Publishers: False Positive also Exists: Keep it in Mind when Dual Test is Performed
JUNIPER PUBLISHERS- JOURNAL OF GYNECOLOGY AND WOMENS
HEALTH
Journal of Gynecology and Women’s Health-Juniper
Publishers
Authored by Juan Piazze*
We report two cases of false
positive results regarding Dual test for first trimester non invasive
diagnosis of chromosomopaties, describing how different paths may be
present even with simile parameters, in two different pregnant women.
Introduction
The Down syndrome is a congenital disorder which verifies when a a trisomy of 21th chromosome is present (T21). In Italy, 1 neonate over 700-1200 is born under this condition, which presents a variable degree of retardation in mental and physical development, other than the presence of other congenital malformations [1].
The prenatal diagnosis includes the analysis of fetal
cells caryotype (blood or amniotic fluid) or from throphoblast
(villocentesis) and a non-invasive procedure, the Dual test, which is
performed when CRL ranges between 45 to 84 mm within 11 to 13+6 wks
gestation [2]. The Dual test is an association of fetal nuchal translucency (NT) plus the evaluation
of maternal free-BhCG and PAPP-A (detection rate 85-90%, false positive
rate 3-5%). This Dual test may be enhanced by the evaluation of other
ultrasound parameters such as the nasal bone, the ductus venous and the
tricuspid regurgitation. In Italy, and as suggested by the SIEOG, the
prenatal screening must be proposed to every pregnant woman, independent
form age at the moment of examination. This information may be offered
not only by gynecologist but also by midwives and the Family Doctor, or
even by means of written material. Regardless of the prenatal diagnosis
chosen, if a high risk is found (considered 1/250), the pregnant woman
must be informed regarding the possibility of an invasive prenatal
diagnosis, which includes the villocentesis in the first trimester and
the amniocentesis in the second trimester [3].
We report two cases of false positive results
regarding Dual test for first trimester non invasive diagnosis of
chromosomopaties, describing how different paths may be present even
with simile parameters, in two different pregnant women.
Cases
Two pregnant women were referred to our department
for a first trimester evaluation and for the strategy regarding the
pregnancy follow-up. We underline the similarity in both women, one 33
(lawyer) and the other 32 year old (school teacher), both in second
pregnancy with the first baby born under spontaneous delivery and in
good neonatal conditions.
In both cases the Dual test was proposed and
performed within the twelfth week gestation as stated linked to an
optimal period for this method execution. After the Dual test responses
were ready, both pregnant women presented the same peculiarities: nuchal
translucency at 95° percentile and both maternal serum parameters
altered. If just NT were altered, an evaluation of maternal blood free
placental DNA (cfDNA) would be proposed [4],
if both parameters (NT and maternal serum) were altered, an invasive
prenatal diagnosis procedure would be proposed. So the gynecologist and
both the pregnant women decided to perform the amniocentesis between
16-18 wks gestation. And this is where this presentation changes, in one
of the cases, every doubt was solved serenely, and the pregnant woman
tried to solve every doubt or eventual risk directly with the
gynecologist help.
In the other case, the 32 year old pregnant woman
looked for other physicians suggestions (not gynecologist colleagues),
and was constantly in contact with other women with amniocentesis
recommended after altered Dual test, in the deleterious internet forums.
But what the other pregnant woman absolutely did not do: the 32 year
old woman made take a look of the Dual test response to a statistician!
When we observed these two ways of facing the same
problem in two healthy women, we decided to face the truth and underline
the only argument that may have tranquilized both of them, the false
positive rate of about 3-5% regarding Dual test procedure. The 33 year
old took took a breath in her preoccupation, and the 32 year old went
deep into the fact: “but are you sure, is it more a 3% or a 5%?”
What followed was absolutely the same in both cases,
amniocentesis performed uneventfully, two normal caryotype fetuses in
which a structural ultrasound examination by middle gestation and an
echocardiography were performed showing two pregnancies in absolute
maternal-fetal health conditions; both of them now by 32-34 wks
gestation.
The final analysis
The lawyer with a permanent laugh, the other lady
facing the physicians group telling us: if you knew that false positive
exists, why did you make me perform the Dual test!
Comment
This more than a serious case-report, is a report of
our clinical experience regarding the behavior of two women with the
same risks, in simile conditions; that may not be absolutely the same.
When the 32 year old school teacher talked about the
statistician that reviewed the Dual test response, we understood the
female’s world is certainly a wonderful unknown universe. And a pile of
clinical practice reflections, women to whom an altered test is
explained, are not acquainted with new terms (i.e. diagnostic accuracy,
false positive, detection rate, multiple of median, sensibility, etc.).
Some of them may accept what we try to explain, the 32 year old pregnant
woman is an example that this may not always happen and that, at the
end, she did everything in order to convince herself that her baby was a
healthy one, fruit of that blessed false positive rate.
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