- [Voiceover] So we all have that friend,
that one friend who is never in the right place
at the right time.
Well it turns out that placentas also have that one friend.
So what do we mean by that?
Well placentas are normally located in the upper part
of the uterus.
So near this portion of the uterus called the fundus,
the fundus.
And there's this condition called placenta previa,
placenta previa, in which the placenta
is abnormally positioned.
So instead of being found in the upper part of the uterus,
it's found somewhere in the lower part of the uterus,
kind of like this, near the portion of the uterus
called the cervix.
So instead of being found in the fundus,
it's found near the cervix.
And the placenta can either partially or entirely
cover up the internal opening to the cervix,
so this portion right here called the internal os
or the internal opening of the cervix.
So why does this happen?
Well it turns out that the placenta will form
wherever the embryo implants.
So if instead of implanting near the top of the uterus
like it's suppose to, the embryo implants
in the lower part of the uterus,
the placenta will also form in the lower part of the uterus,
leading to placenta previa.
So if you look at this diagram, you might ask yourself,
well yeah sure the placenta is located in the wrong place,
but is that necessarily a bad thing?
And the answer to that is sometimes.
So early on in the course of a pregnancy,
if a woman is diagnosed with placenta previa,
it tends to not be that big of a deal,
and the reason for that is
because as the pregnancy progresses the baby grows
and as the baby grows the uterus gets larger
and it stretches out.
And with the stretching out of the uterus,
the placenta gets dragged along to a higher position.
So if a woman is found to have placenta previa
early on the course of her pregnancy,
as the uterus grows, the condition tends to self-resolve,
and the placenta tends to find itself in a normal position
by the end of the pregnancy,
so much so that it's pretty rare to still have the condition
by the time the baby is ready to be delivered.
So for that reason, if a woman is found
to have placenta previa early on in her pregnancy,
it tends to not be that big of a deal.
If however, she's found to have placenta previa
later on the course of a pregnancy
or if she was found to have it earlier on
and it still persists by the time
that she's ready to be due,
it tends to be a very big deal.
And the reason for that is that in this location
the placenta is really prone to bleeding
and I want to show you why that is.
So I kind of want to expand this or zoom into
this part of the uterus.
So we already talked about the structure of the placenta
in another video that's called, Meet the Placenta.
So over here we're just briefly going to gloss over it.
So this is the uterus or rather it's the wall of the uterus
and the uterus is a muscle, right?
It's a muscular organ.
So in a non-pregnant woman there are all these blood vessels
or arteries, they're called uterine arteries
that come down to the uterus and they supply it
with oxygenated blood.
Because again, the uterus is a muscle
so it needs lots of oxygen.
So what happens in pregnancy is that these uterine arteries
become really juicy and plump
and they actually cross through the wall of the uterus
and they squirt out all this blood.
Kind of like we said the jets in a hot tub do.
And they squirt out all the blood into the placenta.
So the placenta is kind of like a pool of blood
and the baby also sends down blood vessels into the placenta
so that it can get access to all the oxygen
and the nutrients from the pool of blood
that is the placenta.
So something pretty amazing happens late
in the course of the pregnancy
when the baby is pretty close to being delivered.
So as you might know, if you look at this diagram over here.
So as you might know, when babies make their exit
from the uterus, they do so head first,
and their heads tend to be pretty big,
and you can see that this thick and plump part
of the uterus, the cervix,
is kind of standing in the way of the baby's head.
So what happens towards the end of the pregnancy
is that the wall of the uterus over here, at the cervix,
thins out to widen the passage for the baby.
Now normally this is a good thing.
It's an awesome thing,
but if the placenta is sitting right here
like it does in placenta previa,
it can be a pretty dangerous thing.
So when the wall of the uterus thins out,
the attachment here, the attachment between
the uterus and the placenta is actually strained.
It starts to become weakened and the placenta
starts to detach.
And as you can imagine these uterine arteries,
which are actually in the wall of the uterus
are being tugged on in this direction
as the wall thins out,
but since they're also attached to the placenta,
they're also being tugged on in the opposite direction.
So pretty easily the tension on these arteries
can cause them to rupture
and blood leaks through into the vagina.
That's actually how placenta previa tends to present
with vaginal bleeding late in the course of the pregnancy
so that's called antepartum bleeding,
so antepartum vaginal bleeding.
And antepartum refers to the portion of the pregnancy
that's after the 20 week point.
So it turns out that there are two major causes
of antepartum bleeding.
One of them is called placental abruption,
which is something that I'm going to talk about
in it's own dedicated, committed video,
and the second cause is placenta previa.
And there's a really important way to tell them apart.
So placental abruption tends to present
with painful bleeding
where placenta previa tends to present
with bleeding that's not so painful,
so painless vaginal bleeding.
So if a woman presents with painless antepartum bleeding,
so painless vaginal bleeding after 20 weeks
into her pregnancy, she's suspected of having
placenta previa.
And if that's suspected,
if placenta previa is suspected,
the very first thing we do is an ultrasound,
so we slap an ultrasound onto the belly
to visualize the location of the placenta.
And if the woman is found to have placenta previa,
it is really important.
We make a pretty big point not to do a pelvic exam,
so not to insert either a speculum
or a finger through the vagina,
and that's because either of these two maneuvers,
inserting either a speculum or a finger through the vagina
can cause or it can worsen the vaginal bleeding.
Okay, so if a woman has placenta previa, what's next?
Well a lot of that depends on what she looks like
when she presents.
So if she comes in with pretty minimal vaginal bleeding
and she's hemodynamically stable,
so if her blood pressure and her pulse are okay,
then she's probably going to be sent home on bed rest
and she's going to be told to avoid
strenuous physical activity
and to avoid sexual intercourse
because that in of itself can cause bleeding.
And then she'll probably be brought back to the hospital
around 34 weeks into her pregnancy to have a C-section
and the reason why we choose to do a C-section
rather than proceed with a vaginal delivery
is pretty apparent in this diagram.
So remember when we said that
the baby passes through head first,
so you can see that the placenta, in placenta previa,
is blocking the baby's path,
and during delivery the strength of the uterus contracting
and pushing on the baby through can shear the placenta,
which remember is a pool of blood pretty much,
so that can cause massive hemorrhage for the mom,
so that's why we offer a C-section
to avoid this potentially fatal situation for the mom.
Now if instead the mom presents with massive bleeding
and she's hemodynamically unstable,
so if her blood pressure and her pulse
are not doing so okay,
then we go in for a C-section at that time
regardless of how far along her pregnancy is
or how old the baby is to prevent any consequences
for the mom.
So I guess that leaves us with a pretty important question
and the question that a lot of people tend
to be interested in and that is
what increases your chances of having this condition?
And one of the biggest risk factors I guess you can say
is having a history of placenta previa.
So if you had placenta previa with a previous pregnancy,
you're much more likely to have it
with any future pregnancies.
Another pretty big risk factor is multiple gestations,
so women who have twins or triplets or quadruplets
or more babies, because each of these babies
has its own placenta and you can imagine
that the higher number of placentas,
the greater the chances of having one fall into this area.
Alright, so it's simply a probability game.
And there are a few other risk factors
like having surgery on the uterus
or having a uterine scar that'll increase your chances
of having placenta previa.
So there you have it, placenta previa
or the placenta that's never in the right place
at the right time.