Okay. That’s one of the things
that can go wrong. But one
of the things that can go right is the modern
approach to assisted reproductive technology.
Now that we understand these events relatively
well, the possibility of intervening to help
couples to have children has been very important,
and since the first test tube baby has been
born, there have been very many test tube
babies that have brought joy to parents in
a variety of different settings.
So, in vitro fertilization is one of the key
aspects of assisted reproductive technology.
Here, what happens is that egg production
is stimulated hormonally in the mother, and
then some eggs are harvested. They’re actually
removed under ultrasound guidance from the
mother at stages when they’re capable of
being fertilized. They are placed in a dish,
not actually in a test tube of course but
in a small millimeter dish filled with a rich
culture medium. And then sperm from the father
or from a donor is added to the dish and fertilization
can take place within that dish itself. Subsequently,
the eggs are observed. There may be video
recorded in a real IVF clinic, for instance.
And the ones which are developing well to
schedule, you might be looking at them at
the two-cell, four-cell stage to show that
they’re dividing as normal as you would
expect them to do, can then be returned to
the uterus, and there, they will have a respectable
chance of implanting and development taking
place as normal. Nowadays, it’s traditional
to transfer only one egg back into the uterus.
Previously, more eggs were returned to the
uterus and that meant that sometimes you got
twin pregnancies or even triplet pregnancies
if three eggs were returned. The reason that
that’s no longer so popular is that twin
pregnancies are always just a bit more challenging
than a normal single pregnancy. So the risk
of something going wrong with one, or indeed,
both the twins is greater than it is with
a single pregnancy. So in the early days,
as this diagram shows, then perhaps three
embryos might have been returned, but no,
that’s actually much less common than it
was done previously.
In addition, you can help the process. As
we’ll see in the fertilization lecture,
it’s possible to actually inject sperm through
the zona to ease their passage. Eating their
way through the zona is quite a tricky task
for the sperm, and it may be that some occasions
of failure to conceive normally has been as
a result of the sperm not being able to make
its way through the zona. You could also inject
a cell or inject the sperm directly into the
egg. So it doesn’t even have to cross the
cell membrane of the egg, and each of those
gives ways in which the whole process of fertilization
can be enhanced and advanced in appearance.
You might not otherwise be able to do that
spontaneously and naturally.
You can also, at these early stages; you can
screen for genetic defects and select which
of the fertilized eggs will be re-implanted.
So, that can be a choice. An easy one, for
instance, would be to identify whether the
developing pre-embryo is male or female in
a family which is liable to, muscular dystrophy,
Duchenne muscular dystrophy then it’s passed
on through boys alone. So returning female
pre-embryos to the uterus would mean that
you do not have a child that suffered from
muscular dystrophy of that particular kind.
A recent development in the UK has been used
of three parents’ IVF where the egg cytoplasm
from one mother is combined with the nucleus
from the second mother and sperm from the
father, and that’s to avoid disorders of the
mitochondria which are present in the cytoplasm.
So, a radical new technique to avoid
some inheritable defects.
So, let’s summarize what we’ve looked at in this lecture.
First of all, we looked at the early division
stages, the cleavage stages in which the cells are
getting smaller at each subsequent cell division.
And then we looked at the process of hatching
from the zona pellucida.
Once it’s hatched from the zona pellucida, then
the developing pre-embryo can implant into
the uterine wall, and gradually, begin to
eat its way under the surface. If this process
takes place in the wrong place too soon, then
we can have the serious risk of an ectopic
pregnancy, which can, in fact, be life threatening.
But the good news is the understanding this
processes well as we do know, has allowed
us to develop all kinds of reproductive technologies,
which can bring childless couples the possibility
of having natural children of their own.
Thank you very much.