the major body structures being formed and
laid down at that point. Now, I’ve said
several times that things might go wrong.
So let’s explore that in a little more detail.
I’m going to ask some questions and offer
answers as best we can. There is still much
that we do not know about this complex and challenging
area of development, and indeed,medicine.
So we’ll look at how common they are, and we’ll
look at the forms that major
abnormalities can take. We will make our best
guesses as to what may cause them, and there
are three categories; genes, substances or
teratogens, and unknown factors. Then we’ll
look at the timing for teratogens for agents
which might cause abnormalities.
And then we’ll look at the nature of them. We’ll
comment on how people might feel about this.
This is a very sensitive and very important
area. It often worries the expectant parents
greatly. They’re worried that something might
be wrong with their baby. And sometimes
that can lead them to feel guilty when, of
course, there is no cause for them to feel
guilty about something that happened to their
baby. Then finally, we’ll look at how frequency
can be reduced, and that would feedback into
our initial question of how common they are.
Fortunately, in Western Europe, the frequency
of developmental abnormalities has been falling,
and there’s every reason to expect that
we could make it fall still further in the future.
So, how common are developmental abnormalities?
The answer is they’re actually much more
common than people realize. In Western Europe
where rates are relatively good, about 2.5%
of all babies have a significant developmental
abnormality detected at birth. That’s one
baby in 40. That’s far more common than
people, even sometimes doctors realize.
And we’re actually speaking about abnormalities
which might have an effect on function if
you’re to look at minor variations. Well, to be
honest, almost everybody has minor variations
of one kind or another. But in addition to
that, there’s another 2.5% that are detected
in infancy and childhood. So, there are things
like deafness, for instance, which may not
be detected at birth, or problems with movement
which become evident when the child when the
infant starts to walk. At that point, heart
defects can also become detectable because
the extra work required from the heart might
show up a problem that had previously been
undetected. In addition to that, an unknown number
of fertilizations do not lead to pregnancies.
They terminate spontaneously after fertilization
has taken place. Now obviously, if fertilization
does not lead to a pregnancy, it’s very
hard to know that it happened at all, and
therefore, that’s why we’re not sure about
the total number. The highest estimate I know
is that perhaps 75% of all fertilizations
terminate spontaneously. And if one ever manages
to retrieve one of those fertilizations, it
looks as if it’s the genetic cause that
something significant has gone wrong with the
genetic expression in the developing fertilized
egg and that it has terminated itself spontaneously
as a result of that. As I said, that’s something
of a guess and we don’t actually know exactly
what proportions do terminate. We merely know
that it’s a significant proportion.
Of course, we haven’t looked at complex
problems, which are not detected until much
later in life. So, there is already evidence
that things that happened during the fetal
period can have an influence on how likely
you are to have a number of conditions as
an adult, and that includes cancer and diabetes,
heart disease, and even possibly mental conditions
such as schizophrenia, something has happened
in the course of development which has increased
the chances that you will suffer from these
as an adult and at the moment, we have very
little idea of what these factors affecting
the pregnancy might have been. But obviously,
the implications of these are massive, and
if we could tell what those factors were,
we might have another way of addressing these
adult illnesses during the early stages of development.
Now this is a table from a survey
of abnormalities in Western Europe and you
can see that the rate here is expressed per
10,000 pregnancies. So 256 per 10,000 means
that that’s our 2.5% that we spoke about
previously. And looking at the frequency of
each of these, you can see that congenital
heart defects are the most common single kind
moving down through limb defects, defects of
the urinary system on and then the nervous
system. And part of that includes neural tube
defects. So they come under the total of our
nervous system through the digestive system,
things affecting the face, and then things
affecting the respiratory system and then
the eyes and the ears. So those are the most
common ones. The table on the right-hand side,
the column on the right-hand side, are the
same figures but excluding non-chromosomal
causes such as Trisomy 21 Down syndrome.
You can see that the non-chromosomal defects contribute
a small part, but only a small part to the
overall frequency of the developmental defects.
People have interpreted these in complex and