Now, I mentioned ectopic pregnancy.
As we’ll see in another lecture, fertilization
takes place actually, quite
near the ovary; the egg is shed from the ovary
near the mouth of the oviduct shown in pink here.
And the sperm has to swim all the way through
the vagina up through the uterus and
then along the oviduct in order to reach the
egg, and fertilization takes place at this
end of the oviduct. Then the fertilized egg
begins to get wafted back down the oviduct
towards the uterus. Normally, as we’ve seen,
it will implant in the walls of the uterus.
And the function of the zona pellucida among
others is to stop implantation taking place
too early. These outer cells of the syncytiotrophoblast
are actually very aggressive and they will
invade tissue with enormous enthusiasm. Normally,
they have to be safely in the uterus where
the walls are thick and ready to receive it
to avoid the risk of causing any damage.
If hatching takes place prematurely, or if the
embryo is delayed in this process down the
oviduct in any way, then there’s the risk
that it might implant in the wrong place.
The most common place for it to implant is
actually in the oviduct itself. So you have
a tubal ectopic pregnancy. The percentages
shown in the diagram indicate where the most
common kinds of ectopic pregnancy may actually
be. Now, this process of implanting in the
wrong place, this ectopic pregnancy can occur
in as many as 1% of all pregnancies and therefore,
it’s a relatively common event and one which
is serious and potentially life-threatening.
If it was undetected and the developing pre-embryo
reached a major blood vessel, then that rupture
could lead to the mother bleeding to death.
So if you are thinking of studying medicine,
it is the kind of thing that you would need
to be very alert and aware of. So, what might
we look for? Well, what would normally happen
is that there would be some abdominal pain
associated with the process, and also perhaps,
some vaginal bleeding. In addition, there
might be referred pain. Now, referred pain
is an unusual phenomenon which you might not
be familiar with. But the idea is that your
insides are actually not very well supplied
with sensitive nerves. And pain, something
going wrong within that, might be referred
by the nervous system to some other part of
the body, for instance, the tip of the shoulder.
So if a mother presented with some vaginal
bleeding and pain in the tip of the shoulder,
one of the things that you might want to think
about is the possibility of an ectopic pregnancy.
Under those circumstances, what you might
want to do is to carry out a pregnancy test
to check if she’s in the early stages of
pregnancy because, of course, at this stage,
she wouldn’t probably know that she’s
pregnant at all. And perhaps an ultrasound
scans to see if you can identify where the
pre-embryo is actually implanted.
There are some things which can actually predispose
towards an ectopic pregnancy. So for instance,
if mothers had a previous ectopic pregnancy,
it suggests that there might be an issue perhaps
in transport of the fertilized egg down the
oviduct towards the uterus or if you suffered
from pelvic inflammatory disease, this might
also be a risk factor for an ectopic pregnancy.
Very unusually, astonishingly, sometimes,
ectopic pregnancies will continue as normal.
It might have implanted in the tube, as we
have described as the most common version,
or it might even have fallen out the oviduct
altogether and be lodged somewhere in the
abdominal cavity in the abdominal linings.
In pregnancy, if it doesn’t kill the mother
at these early stages, if it progresses, there
is a very small possibility that the baby
might go towards a stage where it was old
enough to be actually delivered.
Of course, it would have to be delivered by caesarean
section. It could not be born normally because
it’s not in the uterus at all.