Uso cientÍfico del tÉrmino preembriÓn
SCIENTIFIC USE OF THE TERM ‘PRE-EMBRYO’
Director of the Institute of Life’s Science of the Catholic University of
Attempts are often made through semantic manipulation to distort
biological reality, particularly when this has ethical connotations, and above
all if this biological reality is related with new human life, since it should not
be forgotten that it is in that period of time in which the life of a human being
is suffering a higher number of attacks.
In this context, a paradigmatic example of what we have mentioned is the use
of the term ‘pre-embryo’, which, in our opinion, does not have any scientific
basis but does however have clear ideological, when not political
In order to evaluate whether there is indeed a scientific basis for using the
term ‘pre-embryo’, we thought that it would be interesting to analyse the
frequency with which it is used today in biomedical literature, since surely the
frequency of its use will make it irrefutably clear if said term does or does not
define a biological entity with its own characteristics, different to the embryo,
and consequently with a scientific basis to be accepted as a differential stage
With this objective, we reviewed some previous data from the literature which
refer to the term ‘pre-embryo’, but in particular we carried out a personal
review of this topic in the period between 1997 and 2009, using PubMed as a
The term ‘pre-embryo’ was first used in 1986 (1-3), based on the
criterion, arbitrarily proposed in 1984 by the Warnock Commission (4), which
established that human embryos could be manipulable up to 14 days after
impregnation of the oocyte by the sperm cell, although said Commission
admitted, in the same document, that the life of the human embryo begins
However, in our opinion, the use of the term ‘pre-embryo’ is not only a
semantic manipulation aimed at depriving the early embryo of its fundamental
biological characteristic of living human being, but it is also a serious
biological mistake, since it seems to us that there is no scientific reason which
justifies calling the human pre-implantation embryo a ‘pre-embryo’. For most
experts the pre-embryo, biologically speaking, does not exist, so the term that
identifies it as such is becoming less frequently used in scientific literature.
To confirm this, we reviewed how science currently uses the term ‘pre-
embryo’; unsurprisingly, we were able to verify that its use is very limited.
In a review on the use of the term ‘pre-embryo’ published in 1997 (5),
in which the authors used Medline as the data source, they were able to show
that between the years 1991 and 1996, the term ‘pre-embryo(s)’ only appeared
83 times in the scientific literature, compared to 28,434 for the term
‘embryo(s)’. Something similar was observed in another review by Ferrer and
Pastor (6), who analysed the same topic, although on a larger scale. These
authors found, also using Medline as a data source, that between 1991 and
1997, the word ‘pre-embryo’ appeared in the title of scientific articles 55
times (13 in 1991; 10 in 1992; 9 in 1993; 8 in 1994, 6 in 1995; 7 in 1996 and 2
in 1997). On the contrary, the term ‘embryo(s)’ appeared 36,301 times. In
other words, the minority use of the term ‘pre-embryo’ in medical literature is
evident, and not because this area of science is in decline, since together with
the scant use of the word ‘pre-embryo’, we can see the large number of
occasions on which the term ‘embryo’ was used.
However, analysing the use of the term ‘pre-embryo’ from 1997 to
2009, and in this case using PubMed as the information source, it was found
that in those 13 years, the term ‘pre-embryo’ appeared just 20 times in the title
of scientific papers: 2 in 1997 (7-9), 3 in 1998 (10-12), 1 in 1999 (13), 1 in
2000 (14), 1 in 2001 (15), 2 in 2002 (16 and 17), 2 in 2003 (18 and 19), 1 in
2004 (20), 3 in 2005 (21, 22 and 23), 2 in 2007 (24, 25) and 1 in 2008 (27).
This clearly demonstrates the lack of scientific interest currently aroused by
If we look a little more closely at the latter data, of the 20 papers
published which use the word ‘pre-embryo’ in their title, only 16 (8, 9, 11-14,
17, 18, 20-27) were in scientific journals. Furthermore, one of the cases was
published in a local journal (14), and three of the others were reviews (8, 9,
13). Therefore, there were only 12 original articles published during those
years in international journals (11, 12, 17, 18, 20-27) in which the term ‘pre-
embryo’ was used in the title. In other words, 0.92 times per year. Moreover,
if we take into account that three of the 16 studies reported (18, 20, 23) were
from the same group, it can be stated that, in reality, only 13 scientific groups
have used the word ‘pre-embryo’ in the title of an experimental study during
Another interesting aspect to consider is that none of them were
published in leading scientific journals (those with an impact factor greater
than 15), top quality journals (impact factor between 10 and 14) or even
comparative journals (impact factor between 5 and 9). Only 10 (11, 18, 20-27)
were published in mid-quality journals (impact factor between 3 and 4) and
the other two (12, 17) were in journals of a lesser scientific standing (impact
In summary, the above data support the finding that the term ‘pre-
embryo’ is practically outside the current scientific context, and that its use, in
most cases, has a more ideological than scientific connotation, all with the aim
of depriving the embryo of its ontological status of living human being, to thus
be able to manipulate it without greater ethical responsibility.
Key words: Pre-embryo, implantation embryo and human embryo.
Certain scientific bodies and some social groups occasionally promote the use
of the term ‘pre-embryo’ to designate pre-implantation embryos. Given that
the use of said term appears devoid of the most fundamental scientific basis,
we reviewed its use in the specialised literature during the years 1997 to 2009,
confirming that the use of the term ‘pre-embryo’ is minimal; consequently, we
consider that there is no objective reason to continue using it, and that when it
is used, this may be motivated more by ideological interests than by scientific
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