The Placenta and Umbilical Cord - HD

Introduction to the Placenta

Hello, I'm Dr. Paula Woodward from the University of Utah.

And today I'm gonna be discussing the placenta with you.

Today we're gonna talk about the placenta and I was also assigned the umbilical cord, but because of time, we're really gonna focus on the placenta.

And the placenta is really a fascinating organ in that in your entire life, it's the only organ that it's time limited and disposable.

Also, it's the only organ that you actually share.

It's both from fetal and maternal origin.

Now in a legal dispute, the fetus would win on this because the larger portion actually is formed by the fetal corion.

But the endometrium plays a key role in the decidua basalis.

The placenta has many important functions.

It's a physiologic barrier.

This is where all the gas nutrient exchange occurs, and it also has important endocrine functions.

Embryology of the Placenta

Now I wanna start by talking a little bit about the embryology.

And we all know fertilization occurs here in the tube and cell division starts as it travels down the tube till you get this cell bundle.

This ball called the moula.

And that moula starts to differentiate into a bottom layer and a outer layer here.

And that's the blast assist.

And it's this blast assist from which the placenta will start to form.

The blast assist has several layers to it.

First of all, inside you have the embryo blast.

All right? And that's gonna be the embryo.

But we really wanna pay attention to the outside here.

And it's got two parts to it.

We have this outer smooth part, which is the cytotrophoblast, and then this inner cell layer, the syncytiotrophoblast.

Now this is a very aggressive group of cells.

The membrane starts to break down between them.

They're burrowing into the endometrium in a very aggressive fashion, they become multinucleated.

And what have I just described?

I've just described a very aggressive tumor.

And this is really what this is acting like.

But it is fascinating that it is limited just to the endometrium and does not go beyond, at least in a normal situation.

What happens with that sensio trophoblast, it starts breaking down these little capillaries in the endometrium and they form these little lacuna around it.

And that's actually what's going to give the developing embryo nutrition and tell the placenta actually forms.

Now that's the syncytiotrophoblast.

But then we have our cytotrophoblast, that small ring on the inside, and it starts to push out here and starts to make these little VII going all around.

And that's gonna be very important as the placenta starts to develop.

Early Ultrasound Findings

Now let's look at what we're seeing on ultrasound, because at this stage we see what we call the intertidal sac sign.

And that is that little sac is buried within the decidua.

Now just a moment about terminology, decidua belongs to the mom.

It's the endometrium.

Now, as that grows, we can see, even though we don't see anything in there, there actually is a lot of important structures.

We have the primary yolk sac, the secondary yolk sac, the embryo blatt is right here.

It's just below our level of resolution.

As the sac grows, we get what we all know as the double decidual sac sign, where we have the base sali at the bottom of the sac, the capsularis forming a capsule of the sac, very good names.

And the paral is the remaining.

And that gives you the double decidual sac sign.

And we can see that decidua very nicely on first trimester scan with the basalis, the capsularis, the parietalis.

And this hypoechoic area between the two is the remaining endometrium.

But very quickly, this wall will coapt against that one.

And we have a single sack, and we never see these again.

Development of Chorionic Villi and Membranes

Now let's look at what's happening with that, those little cho villi that we started to see develop.

First of all, choon is the embryonic trophoblast, all right?

And the chorionic sac is really what we refer to the gestational sac.

All right? And so there's the choon all the way around.

Well, this Choon has one job.

These chorionic villi need to seek nutrition and quickly they figure out there's not much blood supply up there.

So they start to involute on that side, making the smooth choon.

And they grow down here into the Deua Bay ssus, which has lots of flow.

And that is the chorionic front doum or the cho villus choon.

Now let's look inside and see what's happening with the embryo.

We have another membrane that's gonna start to form, and that's the amnion.

And it starts as this little tiny slit right by the embryo.

And as it grows, it envelopes the embryo and creates a little sack around it.

Now at this point in pregnancy, we have a small little amnon around the embryo.

So there is the amnion around the embryo.

We have a yolk sac.

Everybody loves the yolk sac.

It's nice and genic and easy to see.

The corion is out here.

And so we have a large chorionic space at this point and a very small embryonic space.

Now, as the first trimester progresses, the amnion enlarges, but it's just this very thin membrane by here.

You can see the umbilical cord is already formed.

Very thin amnion, very thick choon around here.

The yolk sac has been jettisoned because the umbilical cord is formed.

It's out there in the choic space.

And by the end of the first trimester, the amnion and corion approach each other, but they've not yet fused.

That's an early second trimester event.

Notice that the chorionic cavity is often more echogenic.

It's got these very thick rich mucopolysaccharides within it that gives it this echogenic appearance.

So let's now review all our membranes and everything we can see in the first trimester.

And first of all, from the mom, we get the decidua.

We have the paral, capsularis and Bali.

We have the thin little amnion around the embryo.

We then have the smooth corion on top and the villus choon or chorionic fromum at the bottom.

And the villus choon of the embryo with the decidua salus of the mom is what gives us the placenta.

When we look at an actual pathologic specimen, you can nicely see that smooth corion where it's atrophied on the top and the villus corion along the basal surface.

And we can see that when we scan there is the corion, our thin little amnion.

And here's the thickened area, the villus corion, and the decidua based salus, which is going to be the placenta.

We can also see that olein are now starting to form.

Structure of the Mature Placenta

Now let's look at the placenta in its more mature state.

And let's go over again the relative contributions from the mom and the fetus.

And from the fetus, we're gonna see the thin amnion.

We have the thick choon, which now is called the chorionic plate.

And off to the side, the amnion and chorionic membranes are fused off of the chorionic plate.

We had the mainstream mainstem villus, and this is where all the gas exchange occurs.

From the mom side, we had the myometrium and the decidua basalis, which is now called the basal plate.

We have the septa that are project in and they're gonna facilitate venous return between the septa.

We have the co leadin, which we saw developing in the first trimester.

And then we have the intervillous space where gas exchange and nutrient exchange is going to occur.

When we look at the mature placenta here, here's the chorionic plate that has all the fetal vessels on it and the basal plate, which as the maternal contribution of the decidua basalis.

Placental Circulation

Just a word about circulation.

The circulation and nutrition exchange occurs at this main stem villus.

The maternal arterial blood comes in here under pressure and it makes a little spurt into this intervillous space, and it circulates blood around so that once it goes past the villous gas exchange occurs, then the oxidated blood comes into this intervillous septa.

The point here being this is a very vascular area with a lot of high flow in it, and that's something to be aware of when we start to talk about accreta later.

Placental Abnormalities During Development

All right, what are some things that we can see with the placenta during development?

And the first trimester one that we need to be aware of is the chorionic bump.

The chorionic bump is felt to be a little arterial bleed.

And on the chorionic plate side, sometimes you can actually see swirling blood in these.

When you look at real time, the key is that there is an association with pregnancy loss.

If you don't see an embryo at the time of the scan, there's about a 50% loss.

If you have a live embryo, there's still about a 20% loss.

So a chorionic bump is something that we will bring a patient back for, and anywhere from one to three weeks, depending on how big it is and what other things we see.

The other thing we can see in the first trimester is the per gestational hemorrhage.

And you are very comfortable with these.

They're very common about 3%.

And honestly, I think it's probably higher than that.

It seems like we see these a lot.

Often patients are asymptomatic and don't even realize that they have one and they can go anywhere in size.

Here's a small one.

Here's a larger one.

This one obviously resulted in miscarriage.

The chance of loss goes up as the size of this goes up with about a 20% loss for large, with large being defined as greater than 50% of the sac size.

But even those that don't have a loss, it's important to realize that later in pregnancy they can have other symptoms.

There's a high incidence of per gestational hemorrhage in people who eventually develop preeclampsia.

There's fetal growth restriction, hypertension, et cetera.

Second Trimester Hemorrhages and Abruptions

Now if we move into the second trimester hemorrhages around the placenta, we refer to as abruptions and abruptions can occur in a number of locations.

The most common is at the edge of the placenta.

And we all call these marginal abruptions.

Often they're not a big deal.

Here's a little one we saw here.

No problems, no symptoms in this pregnancy.

You can get pre placental hemorrhages when you get those.

They're most often around the cord insertion.

And how they do really depends upon their effect on the umbilical cord.

If they cause any mass effect and decrease in perfusion, that can be an issue.

The ones that we really worry about though are the retro placental hemorrhages.

And here was a large retro placental abruption where most of the placenta was torn away.

This ended in pregnancy loss.

But really what you're concerned about is how much of the placenta myometrial surface is still intact.

Placental Position and Growth

Placenta position is very interesting.

The placenta continues to grow about the first half of pregnancy until it takes up anywhere from 25 to 30% of the uterine surface.

Now, it has a very fascinating growth called tropho tropism and some people call this dynamic placentation.

I think of it as kind of a giant slow moving amoeba that the placenta really wants a good blood supply.

So it doesn't really wanna be down at the cervix.

The cervix doesn't have decidua, it doesn't have a good blood supply.

So the placenta wants to grow into the area where it has a good blood supply and then atrophy in the areas of a poor blood supply.

Now this has been known forever and if you look at some of the traditional Chinese therapies for previa, they used acupuncture and herbs that they thought would stimulate blow to the fundus.

Also, some of these very old texts say to refrain from sexual stimulation or an orgasm 'cause they don't want flow going down to the lower areas.

Placental Umbilical Cord Insertion

Now in addition to documenting placental position, we always wanna document placental umbilical cord insertion.

And you always wanna do that into planes.

'Cause if you look in just one plane, you may be misled to thinking it is central.

When it's really off to the edge, the central and eccentric probably are the eccentric probably is of no significance.

But once you get to marginal, we really need to follow these because if the placenta regresses from this edge, it can turn into a mentis.

Cord insertion and mentis cord insertions have higher morbidity.

They're more often associated with fetal growth restriction.

So here we are.

You wanna document again in both planes so that you're sure it is absolutely in the correct position.

Here is one at 17 weeks that we see inserts right at the edge of the placenta.

Now by 32 weeks, it's actually place presenting under the membranes here and then going under the membranes to go in.

So we've changed from a marginal insert, excuse me, a very marginal insert to a mentis insert.

And you can see that on the growth specimen.

And you can see these are uncovered vessels.

These fetuses often have a higher instance of growth restriction, particularly if you see twins that are sharing a placenta.

Succenturiate Lobe

The other thing that can happen with placental changes is a suction curate load can develop.

So here at 19 weeks we can see here is the placenta.

It's rather thinned in this area.

By 26 weeks, it's very thin and by 33 weeks it almost like looks like two different ones.

And when you look at path, you can see connecting vessels between this, but it's really thin thinned out into just membranes in between this main mass.

And actually it looks like two little lobes there.

Placenta Previa

Placenta previa.

Now, this has caused some confusion in terminology.

I think everybody was very comfortable on a complete preview that we see here.

But this is where people got confused in terminology.

Some people call these marginal partial low lying.

Actually, partial and marginal came from actually physical exam.

And so there was an effort made in an executive summary put out in 2014 that has unified this language or gotten rid of marginal and partial.

And we just either call these placenta previa if it covers the OSS or low lying with it's in two centimeters.

Now why two centimeters?

Well, if you look at the data, it really does support that 'cause greater than two centimeters.

There's really no indication for a C-section between 10 to two.

There's a low likelihood a C-section and some of your the MFMs will watch these and allow them a trial labor, see how they do, but counsel them for possible C-section and less than 10, they are all gonna go on to C-section.

Now, following these again, here is tropho tropism in action that most of these will resolve most of these low lying ones and as to when to follow 'em.

We tend to follow bring ours back at 32 weeks.

There's no point following these every couple weeks 'cause it's a slow process.

But by 32 weeks, about 90% will resolve and by 36 weeks, 96%.

Here's an example of the importance of looking at where the cortis inserting.

So here we have a placenta previa covering the cervix as you can see.

And that has a little high likelihood of resolving.

But if I go just barely to the side, I can see the cord is actually inserting in a very eccentric fashion, really right on the margin.

And as this resolves, you can be left with vessels covering the os.

And that is called a vaso previa.

And this is very important to recognize because this is a life threatening situation if you don't make the diagnosis.

So you can see here on our schematic that the vessels are covering the os in a developmental situation and then inserting into the placenta.

I think it's imperative on every one of your cervix pictures when you're clearing what was low lying and the cord was anywhere near it that you put color doppler on.

And when you put color doppler on, if you put the pulse wave, you can see that's a fetal heartbeat.

And that was a fetal arterial vessel going right over the cervix and vaso previa.

The other way you can get VAs previa is in the setting of a suction curate lobe.

As the placenta thins out in this area, because the blood supply is poor, it doesn't really wanna be there.

It leaves a chunk of placenta on this side, another one on this side.

And you put doppler on and you see we have an fetal arterial flow.

And look at these big ropes of vessels going between the main placenta and the suction curate lobe.

So this is a potentially life-threatening situation if you don't make the diagnosis.

We know there are pitfalls and everybody in the audience has seen the problem with over distension and contractions and in this case there was both.

The tip off is the cervix is way too long.

You know in your heart of hearts that it is ending right here, but you wait a little bit, let the contraction go down, let the mom void, and you can see the placenta ends nowhere near the cervix.

Alright, so this is kind of our background in cervix.

Placental Masses

I do wanna talk about some specific masses that we can see.

We can see both solid masses and sono lucencies.

Solid Masses

Of the solid masses. We're gonna start with the chorio angio.

It's a solid usually hypoechoic mass.

It's very vascular.

Often if they're small it's no big deal.

But if large, the develop fetus can develop hydrops.

Now I think that's straightforward.

The more unusual one is when you get chorio angio mitosis, which are multiple small masses in the uterus.

As you can see here, multiple small masses.

This really does have a high association with complications including poly hydros and growth restriction.

An unusual solid mass that you can see is the placental teratoma.

This is somewhat controversial because it has a lot of features in common with a trap twin and a cardiac twin.

You can see it's kind of an amorphous blob.

Often cystic areas you'll get calcifications in very much like a trapped twin.

The difference is a trapped twin will be floating out in the amnion.

And this is between the amnion and corion trapped between the membranes and it's fed off of the placental vessel.

You can see here the placenta actually coming up and going around this.

Sono lucencies

Sono lucencies are common, aren't they?

We all see them.

We often refer to these as lakes.

And sometimes you can have this nice gentle lake and we're all happy.

Everything's fine.

Sometimes you can see a lot of lakes and that gets our attention.

And then you can see some really scary lakes and that should really get our attention.

So let's start with those nice placid lakes.

We see these all the time, don't we?

Often you can see low flow on gray scale and this is just a blood filled lac c**n.

But the more you get of these when they throw 'em boast, when you get fibrin, there's really a high association with growth restriction.

This was a mom with hypertension and a severely growth restricted fetus.

If the placenta is big and you have lakes, there are a couple things that we should think of.

And one is mesenchymal dysplasia.

And what this is, these are very abnormal vii and stroma and they're very hydric in appearance.

The placenta will be very thick.

You can see cysts, the fetus is off, are often growth restricted.

We can have abnormal dopplers here.

They'll often be associated with preeclampsia.

When you look at the placenta, you can see these little bubbles, these little cysts.

And those represent these very hydrologic villi.

Now, mesenchymal dysplasia does not have an association with aneuploidy, but the thing that you need to realize, it does have about a 20% association with Beckwith wheatman.

And just to remind you, the features of Beckwith wheatman include emale organomegaly including ne hepatomegaly.

And nephro magaly is often one of the most obvious features that we see in a fetus.

And macroglossia with the tongue being able to enabled to be con uh, retracted into the mouth.

Here's a fetus who didn't, or excuse me, a newborn who didn't happen to have an em falle but was macrosomic a huge abdomen from both hepatomegaly and Nephro magaly.

And this little guy was never able to retract the tongue.

And in fact, a tracheostomy was placed, which you can see right here.

The one that we think about with cystic placenta.

Tripley, isn't it?

So everybody's aware of this, but the thing I wanna point out is not all tripley is equal.

It depends really where you get the extra set of chromosomes.

If you get the extra set of chromosomes from the dad, the placenta will be large and cystic.

You get very usually very severe symmetric growth restriction.

And the ovaries will often be enlarged with thecal colonian cyst.

If it comes from the mom, you're not gonna see the cystic placenta.

Now this is the minority, but still possible.

And they get an asymmetric growth restriction.

So here is the classic one from the dad, the diandra, the cystic looking placenta.

There was a very growth restricted abnormal fetus.

There were thecal lutian cysts.

And when you look at the placenta, it has the multiple small cysts throughout it.

Morbidly Adherent Placenta

And now I'm gonna end with the really scary sono lucencies.

And these we refer to as these tornado vessels.

Everybody, you can recognize 'em when you see 'em.

They're very irregular, they're often linear.

They often have very high flow.

And this makes us worry for placenta accreta.

Now this is really a spectrum from an accreta meaning attached to a invasive in increta to perforated through the wall perreta.

But I'll tell you, we have no chance making these subtle differentiations, particularly accreta and in increta and even the pathologists can't make these often.

And we have gone to talking about these as morbidly adherent placenta.

Some people call these placental attachment disorders.

And my institution, we call 'em morbidly adherent placenta.

Now the risk factors for developing this are our C-section scar and placenta previa.

And the number of C-section scars go up.

The likelihood of developing an accreta goes up.

What are we gonna see on ultrasound?

Well, obviously we're gonna look at previa.

We're gonna look at these scary tornado vessels.

We're gonna look at the myometrium at the retro placental clear zone.

But I'll tell you something, this can be hard.

And I just wanna go through a few findings with you.

And I really think the most important thing is to look really, really carefully at the placental myometrial interface.

And here on this Inova scan, you can follow that hypo coic zone.

And then you completely lost it on this transabdominal scan.

Again, there's the myometrium.

You've completely lost it.

We have a little bit more.

We completely lose it there.

Now technique is important in all things.

It is never more important than when trying to make this diagnosis.

I always use a nine linear.

Look at the difference between this four vector and nine linear.

You wanna make sure you go the entire length of the scar and you look for these little areas of invasion.

And that I think is the single most important thing you can do.

One another thing that you can see just kind of on the big scale is the placenta always looks kind of funny.

You'll get kind of this bulge, but it bulges in both directions.

It so the placenta looks just like a little ball sitting down there.

It's not normal looking.

So I find that very helpful.

You need to be scrupulous in your technique.

Here is no pressure.

This place hasn't even had a C-section.

But look, when you put pressure on the transducer, you lose that clear space.

And don't go crazy with the color.

Oh my goodness.

This is what people do is you'll put doppler on there and just like freak out.

'Cause of all this thought, well, this person hasn't even had a C-section that is just normal placenta.

So I know this is something that's described, but vascularity is very subjective.

And unless you're looking at a lot of normals, you're not gonna recognize an abnormal.

And by the way, these are all normals.

These are not accretive.

And remember that basal plate has a lot of flow within it.

So here is an accreta case and everybody looks at that and goes, oh yeah, look at all that flow.

Well, to me that doesn't really look much different than any of the other normal ones I showed you.

What matters to me is looking here on my high res into vaginal scan and looking, I've completely lost my hypo coag cell.

Other things that are described, turbulent gaps, bridging vessels, and here's an accreta case and everybody looks at this and goes, oh yeah, look how scary.

This one doesn't help me back off on the flow.

And what helps me is actually not how much flow, but what it looks like.

And we don't have that smooth arc that we see in normals.

I kinda like looking for the little gaps in the flow.

And then also these are all very high velocity.

'Cause I've cut way back on my gain.

This was not a diagnostic dilemma in this patient 'cause they were had you look at the Foley, what's being put out in the bag here.

Again, what really helps me is my gray scale.

I'm looking at the bladder here and I can see here's the placenta, it looks to transverse and go up into the bladder wall.

And now I have these traversing vessels on my color.

And then you can put it all together, but really depend on your gray scale.

One another pitfall I really wanna warn you about is bladder varice.

Okay?

They're very common.

This patient hasn't even had a C-section, but we see this in the bladder.

This one did have a C-section.

It was sent to us for invasion.

Well, it's non invasion at all.

There's great myometrium and we do see flow in here, but those are just little bladder varices that are very common in pregnancy.

So you've gotta look at the entire picture.

Conclusion

All right, well, so that was a very cursory view of the placenta.

And when you look at the placenta, give it some love.

You've gotta really look around and look for all of these various features.

Thank you very much.