05 March 2014
Non-invasive Prenatal Testing is becoming a primary screening method in pregnancy, states paper exploring the issues behind the new technology
Non-invasive Prenatal Testing (NIPT) is likely to become a
primary screening method for chromosomal abnormalities (such as
Down syndrome) in pregnancy in the future and so greatly reduce
invasive testing and the associated risks, says a new Scientific
Impact paper published today (5 March) by the Royal College of
Obstetricians and Gynaecologists (RCOG).
The Scientific Impact Paper (SIP) looks at the issues
surrounding this new technology including what it currently is used
for and comparisons with invasive testing.
SIPs are produced by the Scientific Advisory Committee at the
RCOG and are up to date reviews of emerging or controversial
scientific issues of relevance to obstetrics and gynaecology.
Fetal genetic testing has until recently needed invasive
diagnostic procedures (amniocentesis or chorionic villus sampling)
carrying a small but significant risk of miscarriage. However since
1997 the presence of cell-free fetal DNA (cffDNA), which comes from
the placenta and can be detected from the first trimester of
pregnancy onwards, has changed practice and is used for detecting
certain conditions.
Obstetricians currently use cffDNA to guide women whose baby is
at risk of haemolytic disease of the fetus and newborn (HDFN), a
condition where antibodies develop in a pregnant woman's blood and
subsequently destroy the blood cells of the baby she is carrying.
It is also used for fetal sex determination in pregnancies at a
high risk of sex-linked genetic conditions.
This paper explores the use of cffDNA for chromosome testing and
possible sources of error in results from this new technology. It
looks at the difference between this technology and current
practice and the advantages and disadvantages of cffDNA.
Advantages include the possibility of detecting, without risk to
the pregnancy, diseases that may have potentially serious
consequences and secondly it is much more accurate than any of the
previous screening tests.
However the disadvantage is that pregnant women may occasionally
be informed of findings of uncertain significance, such as when
there is a discrepancy between the chromosomal makeup of the cells
in the placenta and the cells in the baby, known as placental
mosaicism. This can result in a healthy pregnancy, however, in some
pregnancies it can lead to complications.
The paper also states that due to the high degree of accuracy of
NIPT, even early in the pregnancy, it will become easier to find
out the sex of the fetus at an early stage. This has a number of
socio-ethical implications.
Excellent communication between women and health professionals
is therefore essential to understanding the implications of the
test results, say the authors.
In conclusion, the paper states that this technology is likely
to become a primary screening method for chromosomal abnormalities
such as Down syndrome in pregnancy, and that it will enhance the
information available to pregnant women while reducing unnecessary
invasive procedures.
Professor Peter Soothill, consultant in Fetal Medicine,
University Hospitals Bristol NHS Foundation Trust and co-author of
the paper said:
"Maternal plasma DNA testing is already being used in the NHS
for some conditions and all obstetricians will need to have
knowledge of the counselling issues involved and need to take into
account the issues around the implications of these test results
for women".
"Detection of chromosomal abnormalities such as Down syndrome by
this technology will alter the way that prenatal diagnosis and
screening is delivered in the UK and in time will give women more
information about their pregnancy whilst at the same time greatly
reducing the number of invasive procedures."
Professor Dennis Lo, FRS, Director of the Li Ka Shing Institute
of Health Sciences at The Chinese University of Hong Kong, and
co-author of the paper said:
"It is very encouraging to see the emerging impact of cell-free
fetal DNA analysis for non-invasive prenatal testing. This is a
good example of the translation of scientific discovery into
clinical practice and heralds an exciting era of genomic
medicine."
Dr Sadaf Ghaem-Maghami, Chair of the RCOG's Scientific Advisory
Committee, added:
"The potential for this technology is exciting and will provide
much more accurate results for pregnant women. However, it is
important that there are resources and training for health
professionals offering this testing and an emphasis on discussions
with the pregnant woman before the test about the implications of
the results."
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