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always less than 20%, and generally no more than 10%. In
summary, then, before the advent of IVF, in every instance in
which we knew of the existence of a normal human embryo,
it would have been true to say of that embryo that, unless it
was deliberately interfered with, it would most likely develop
into a person. The process ofIVF, however, leads to the creation
of embryos that cannot develop into a person unless there is
some deliberate human act (the transfer to the uterus) and that
even then, in the best of circumstances, will most likely not
develop into a person.
The upshot of all this is that IVF has reduced the difference
between what can be said about the embryo, and what can be
said about the egg and sperm, when still separate, but considered
as a pair. Before IVF, any normal human embryo known to us
had a far greater chance of becoming a child than any egg plus
sperm prior to fertilisation taking place. But with IVF, there is
a much more modest difference in the probability of a child
resulting from a 2-cell embryo in a glass dish, and the probability
of a child resulting from an egg and some sperm in a glass dish.
To be specific, if we assume that the laboratory's fertilisation
rate is 80% and its rate of pregnancy per embryo transferred is
10%, then the probability of a child resulting from a given
embryo is 10%, and the probability of a child resulting from an
egg that has been placed in a fluid to which sperm has been
added is 8%. So if the embryo is a potential person, why are
not the egg-and--sperm, considered jointly, also a potential person?
Yet no member of the pro-life movement wants to rescue
eggs and sperm in order to save the lives of the people that they
have the potential to become.
159
Practical Ethics
Consider the following, not too improbable scenario. In the
IVF laboratory, a woman's egg has been obtained. It sits in one
dish on the bench. The sperm from her partner sits in an adjacent
dish, ready to be mixed into the solution containing the egg.
Then some bad news arrives: the woman is bleeding from the
uterus, and will not be in a suitable condition to receive an
embryo for at least a month. There is therefore no point in going
ahead with the procedure. A laboratory assistant is told to dispose
of the egg and sperm. She does so by tipping them down
the sink. So far, so good; but a few hours later, when the
assistant returns to prepare the laboratory for the next procedure,
she notices that the sink is blocked. The egg and its fluid
are still there, in the bottom of the sink. She is about to clear
the blockage, when she realizes that the sperm has been tipped
into the sink too. Quite possibly, the egg has been fertilised!
Now what is she to do? Those who draw a sharp distinction
between the egg-and-sperm and the embryo must hold that,
while the assistant was quite entitled to pour the egg and sperm
down the sink, it would be wrong to clear the blockage now.
This is difficult to accept. Potentiality seems not to be such an
all-or-nothing concept; the difference between the egg-andsperm
and the embryo is one of degree, related to the probability
of development into a person.
Traditional defenders of the right to life of the embryo have
been reluctant to introduce degrees of potential into the debate,
because once the notion is accepted, it seems undeniable that
the early embryo is less of a potential person than the later
embryo or the fetus. This could easily be understood as leading
to the conclusion that the prohibition against destroying the
early embryo is less stringent than the prohibition against destroying
the later embryo or fetus. Nevertheless, some defenders
of the argument from potential have invoked probability.
Among these has been the Roman Catholic theologian John
Noonan:
160
Taking Lzfe: The Embryo and the Fetus
As life itself is a matter of probabilities, as most moral reasoning
is an estimate of probabilities, so it seems in accord with the
structure of reality and the nature of moral thought to found a
moral judgment on the change in probabilities at conception ...
Would the argument be different if only one out of ten children
conceived came to term? Of course this argument would be
different. This argument is an appeal to probabilities that actually
exist, not to any and all states of affairs which may be imagined
... If a spermatozoon is destroyed, one destroys a being which
had a chance of far less than 1 in 200 million of developing into
a reasoning being, possessed of the genetic code, a heart and
other organs, and capable of pain. If a fetus is destroyed, one
destroys a being already possessed of the genetic code, organs
and sensitivity to pain, and one which had an 80 per cent chance
of developing further into a baby outside the womb who, in
time, would reason.
The article from which this quotation is taken has been influential
in the abortion debate, and has often been quoted and
reprinted by those opposed to abortion, but the development
of our understanding of the reproductive process has made
Noonan's position untenable. The initial difficulty is that Noonan's
figures for embryo survival even in the uterus are no longer
regarded as accurate. At the time Noonan wrote, the estimate
of pregnancy loss was based on clinical recognition of pregnancies
at six to eight weeks after fertilisation. At this stage, the
chance of lOSing the pregnancy through spontaneous abortion
is about 15%. Recent technical advances allowing earlier recognition
of pregnancy, however, provide startlingly different
figures. If pregnancy is diagnosed before implantation (within
14 days of fertilisation) the probability of a birth resulting is 25
to 30%. Post-implantation this increases initially to 46 to 60%,
and it is not until six weeks gestation that the chance of birth
occurring increases to 85 to 90%.