Placenta, Cord and Fluid - SD

Introduction

Hello, I'm Dr. Peter Michael Dubay from Brigham and Women's Hospital and Harvard Medical School in Boston.

I'll be speaking on ultrasound of the placenta, umbilical cord, and amniotic fluid.

I'll be spending the next 45 minutes talking about ultrasound of the placenta, umbilical cord, and amniotic fluid.

These are the parts of the pregnancy that don't go home with the mother or parents.

After all, it's just the baby that does go home with them.

But the placenta, cord, and fluid are very important in terms of promoting and ensuring the health of the baby and also the wellbeing of the mother, especially during delivery.

The Placenta

The main items that we can diagnose on ultrasound related to the placenta are placenta previa, placenta abruption, placenta accreta, and creta, increta, percreta, and chorioangioma.

For all of these elements, especially the first two, I'm going to talk not only about how to make the diagnosis by ultrasound, but at least as importantly, how to avoid some of the pitfalls that can lead to errors in diagnosis on ultrasound.

Placenta Previa

The first item that I'm gonna talk about is placenta previa and the terminology that we use in ultrasound for placenta previa.

Some of the terms that are used at least sometimes are placenta previa, marginal previa, partial previa, complete previa, low lying placenta.

So how and when do we use them? Do we use all of them?

What I'll be talking about over the next couple of slides is how we have decided in my own practice to use these terms, which terms to use and when to use them.

If you take the view of the placement of the placenta and the cervix, the way the fetus might look at it, looking from the inside, especially if the fetus had x-ray vision to look through the placenta at the cervix.

If the placenta covers all or part of the cervix, the image on the left shows what would be a complete previa.

This overall gray area here that I'm outlining is the placenta as would be seen by the baby.

And if the baby had x-ray vision, this is the cervix, and this little is the internal os that's closed.

So this would be a complete previa.

The placenta completely covers the cervix.

A marginal previa is the term for what would happen if the baby is looking and sees the placenta that covers part of the cervix.

This part of the cervix up here is not covered.

This part that you see is a dotted line is covered, and the placenta comes right about to the internal os, which is, again, a closed dot.

In the usual situation, a partial previa is somewhat similar to the marginal previa, but is the case when or that term applies when the internal os is open or dilated.

So this is the dilated internal os that is the entire cervix.

The cervix is partially covered by the placenta, but in addition, the open cervical os is partially covered by the placenta.

This partial previa is something that is not generally relevant to ultrasound.

Rarely it is, but when we do ultrasound, in almost all cases, the internal os is closed.

And if you have a closed internal os, you can't partially cover a dot.

So you can't have a partial previa.

So the terms that we use in ultrasound are complete previa and marginal previa.

And this table that first site looks a little complicated.

It's not really that complicated, indicates when we use the terms previa or marginal previa in ultrasound.

This is a diagram of the pregnant uterus.

There's the baby, there's the black as the amniotic fluid, there's the placenta, there's the cervix.

What's key in terms of our diagnosis is closeup view of this area where the relationship between the placenta and the cervix.

So here it is blown up, right over here on this image.

This is the gray area here is the cervix.

The little white, the dark line is the cervical canal that's closed.

The end of it is the internal os.

And what's critical is the distance between the internal os and the edge of the placenta when it comes to using the terms related to placenta previa.

So that distance is key.

And the way that we use it is shown in the table on the right.

When if the distance from the placenta to the internal os is over 20 millimeters or two centimeters, then we say no previa at any age, 16 to 24 weeks or more than 24 weeks.

That's no previa.

If at the bottom, if the placenta completely covers the os we call it a previa or a complete previa in those situations when it's close, but not there.

So when the distance from the placenta to the internal os is zero to 20 millimeters or zero to two centimeters, from 16 to 24 weeks, we call it a low lying placenta.

And after 24 weeks, we distinguish between a low lying placenta.

We use the term if it's 11 to 20 millimeters, and if it's zero to 10 millimeters, we call it a marginal previa.

And I'll show some examples of all of these on the next several slides.

So here you can see we're measured from the internal os to the edge of the placenta.

It's measuring three, just over three centimeters.

Since it's over 20 millimeters, that's no previa at any stage.

Here we have a distance from the os to the placenta of 15.6 millimeters, 1.56 centimeters.

And so that's in the 11 to 20 millimeter range.

We would call it low lying at any age, 16 weeks.

On up here, there is virtually no distance.

It's a roughly zero or one millimeter from the placental edge and the cervical os.

So that's in the zero to 10 millimeter range.

We would call it low lying, 16 to 24 weeks and marginal previa at 24 weeks or beyond.

And finally, and this is a transabdominal view.

The prior were transvaginal views.

The there is the cervix, the placenta completely covers it.

This is a placenta previa or a complete previa at any age.

So those are the basic uses of the terminology.

Important now to look at are some of the potential pitfalls or errors that can be made in diagnosing placenta previa.

Pitfalls in Diagnosing Placenta Previa

So one pitfall is when the fetal presenting part, which is usually the head obscures the lower uterine segment, if it shadows that part of the cervix or the lower uterine segment, that may lead to inability to diagnose or exclude a placenta previa.

And in those cases, if we were to just say the fetal head is blocking our view, can't tell if there's a previa or not, we wouldn't be doing much good.

We're trying to give definitive and accurate diagnoses to say we can't tell is not doing anybody any good.

So what can we do if the head shadows out the cervix?

Well, here you can see two images, two different pregnancies, two different fetuses.

In both cases, the head shadows out at least part of the cervix here, these are transabdominal views.

There's the fetal head casts a shadow.

Down here, the cervix would be somewhere around here.

We have no idea from this image whether there's a previa or not.

Similarly, in this case, this is sagital view low.

There's the baby's head, a little bit of amniotic fluid.

You can see part of the cervix, part of it is shadowed.

We just can't see things well enough to decide whether or not there's a previa.

So what do we do? Do we send the patient away and report that we can't tell?

Well, again, that wouldn't be doing anybody any good.

But fortunately there are things that we can do to get an answer.

So what we would do in these cases is try and push the baby's head up and in, as you'll see in a minute, in both of these cases, I was scanning with my right hand.

I used my left hand to try and lift the baby's head.

And once the head was lifted out of the lower uterus, I could tell.

So watch what happens on the image on the left.

When I push and the head goes up, and when the head is up and away, like right now, there's no placenta.

So by pushing up, we get an answer to is there a placenta previa?

The answer is no, no previa.

On the other case, when we push up, there's the placenta right over at least part of the cervix.

So this is a placenta previa, at least a marginal, maybe even a full previa.

So it's a previa.

So we answered the question by manually lifting the fetal head.

So if you can lift the head, you can avoid the pitfall of having to give a non definitive diagnosis.

Where you is just say, you can't tell another potential problem or pitfall is an overly full maternal bladder.

The overly full bladder may push together, squeeze together the anterior and posterior walls of the lower uterine segment, which can simulate the cervix and lead to a false positive diagnosis of placenta previa.

And here is such a case.

Here on this image, this is a transabdominal view.

There's the placenta, amniotic fluid.

This looks like the cervix.

And if so, the placenta is covering good part of it, right about to where you'd expect the os to be.

So this would be at least a marginal previa.

But the reason that you have to be very careful here that you're not making a mistake is that the bladder is extremely full.

And if the bladder is extremely full, maybe this is not all the cervix, maybe some of this is the uterus pressed together.

So what do we do? We have the woman partially empty her bladder.

And when that's done here, we've gone to a partially empty bladder.

And now you can see the placenta, which ends right around here, is well away from the cervix.

There's no previa, so this was this image you could call a pseudo previa or pseudo placenta previa due to an overfilled maternal bladder.

Yet another pitfall in diagnosing placenta previa is when there's a lower uterine segment contraction, which distorts the lower uterine segment near the cervix, and can cause a false positive diagnosis of placenta previa, as you'll see in a minute on one of these cases.

So here are two different pregnancies.

They both look quite similar.

And at first site, you would think that you're looking at a placenta previa.

So on this case, here's the placenta.

This is, you'd think is the cervix and the placenta covers at least some of it, if not all of it.

So you'd think there's a previa.

Similarly here, there's the placenta.

The internal os you might think is right around here.

So it's covering it or coming right up to it.

Another previa you would think, but you have to be very careful on both of these cases and on cases like them, note that you have these rounded bunched up areas just adjacent to the cervix right here and here on this image.

Big bulge here, and a smaller bulge here.

When you see these bulges, you're dealing with uterine contractions.

And when you're dealing with uterine contractions, you can't tell whether there's a previa.

Everything is distorted.

So what do you have to do?

Well, don't even try to determine whether there's a previa on these pictures.

Don't spend any time.

You just can't tell.

What you have to do when this happens is wait a few minutes for the contraction to go away, and then when the contraction goes away, you'll be able to tell whether it's a previa or not.

Here's what happened on these two different cases.

When we waited for the contraction to go away here on the case, on the left contract, this looked like a previa.

But when the contraction went away, there's the cervix, placenta ends here.

It's not a previa.

On this case, it looked similar during the contraction, when the contraction goes away, you can see that the placenta covers part of the cervix right up to almost to the cerv, almost up to the internal os.

So this is a low lying or marginal placenta previa.

So the way to avoid the pitfall of a uterine contraction is to recognize that it's present by seeing these rounded bulges by the cervix and waiting for them to go away.

So in these cases, the lower uterine segment contraction does not permit assessment for placenta previa.

So when we wanna get an answer to the question of whether or not there's a placenta previa, we begin by scanning transabdominally through a partially full bladder, the partially full for the reasons that I mentioned earlier.

And not a full bladder.

If the baby, especially the head obscures the lower uterine segment, try to manually lift the head.

And if you are unable to lift the head, we go right to a transvaginal scan to take a look at the relationship between the placenta and the cervix.

We used to scan transabdominally, but we have stopped doing so in recent years.

And if we can't lift the baby's head and it's in the way we go right to a transvaginal scan.

Placental Abruption

Let's move from placenta previa to placental abruption.

There are three main ultrasound appearances with a placental abruption.

One is seeing a hematoma under the placenta between the placenta and the wall of the uterus.

That's the wall of the uterus here.

That's the placenta, that's the hematoma.

A second appearance of a placental abruption is a hematoma that extends mostly under the membranes.

Here's the membrane.

Placenta extends under it.

A bit of it is under the, the hematoma extends under it, a bit of the hematomas under the placenta.

But or even in some other case, it may be all under the membranes.

That's another appearance that you can have with a placental abruption.

A third appearance, and this is the one you have to be careful about, is that an ultrasound can look completely normal with a placental abruption.

For example, if the placenta separates from the uterine wall, which is an abruption, but no hematoma collects, the ultrasound is likely to be completely normal, and you don't have to have a hematoma to have an abruption.

So here is an example of a retroplacental hematoma.

This whiter area is the placenta.

This dark area is the amniotic fluid, but this dark area behind the placenta is a hematoma.

So this is an abruption with a retroplacental hematoma.

This is the submembranous version of the hematoma here.

This area right here is the hematoma.

Most of it is just under the membranes.

A little bit of it raises up the edge of the placenta.

Pitfalls in Diagnosing Placental Abruption

So what are the pitfalls in diagnosis of placental abruption?

So one is that if it happens that the hematoma is isoechoic to the placenta has the same echo pattern and echogenicity as the placenta, it may be difficult or impossible to see.

A hematoma that is isoechoic to the placenta can be mistaken for the placenta leading one to miss an abruption.

And here's an example.

If you look at this at first sight, it looks like there's no abruption, no problem.

This is a sagittal view through the fundus of the uterus.

The placenta looks like goes around the fundus like so and like so.

But the person doing the scan was very observant.

And they said that this area here looks different than the rest of the placenta.

Similarly, this area looks different than the rest of the placenta.

Maybe it's not the placenta, maybe it's a hematoma.

So they did two things.

They threw color on.

They turned the color on, which shows that in the part that clearly looks like it's the placenta, there is color flow in the part that looks different.

There's no color flow.

They also watched while the baby pushed up against it.

And you can see that the placenta is quite soft.

This area that you would first think of as a placenta is quite soft, kind of like a hematoma.

Well, they said there's, based on these, even though at first sight you'd think it was normal, they said there's probably a hematoma.

And sure enough, five days later, you can see that hematomas starting to break down, and it clearly is hematoma.

So be careful not to miss isoechoic hematomas.

Another pitfall in diagnosis of abruption are uterine contractions.

Uterine contraction under the placenta can simulate a hematoma, thereby leading to the false positive diagnosis of placental abruption.

So let's look at this image.

When you first look at it, you'd say I think there's a placental abruption.

The edge of the placenta here looks like it's lifted off the wall.

And this at first sight, you might say that's a hematoma.

So the patient has an abruption.

But if you look at it more carefully, the texture of this doesn't look like a hematoma.

And in fact, it looks pretty close to that of the wall.

You might suspect that it's non abruption that this, or a hematoma, that this is instead a contraction.

So if you're not sure, there's an easy way to tell.

Wait a few minutes.

After a few minutes, you can see that this area clearly was a contraction.

'cause it's all gone, looks completely normal.

So this is a normal scan with no abruption, but the contraction could have fooled you for it.

Placenta Accreta Spectrum

Another very important diagnosis not to miss on ultrasound is a placenta accreta or increta or percreta.

They're a continuum in which there's abnormal adherence of the placenta to the myometrium with a placenta accreta the, there's abnormal adherence without invasion of the villi into the myometrium itself, but it adheres abnormally won't come off normally at delivery with placenta increta, there's invasion of the villi into, but not all the way through the myometrium.

And with a percreta, the villi penetrate all the way through the myometrium.

Placenta accreta, or their variants are caused by partial or complete absence of the endometrium, which turns into the decidua during pregnancy.

Normally, in a normal case situation, the endometrium prevents the placenta from coming in contact with the myometrium.

If there is damage to the endometrium, and damage, therefore damage to the decidua, the placenta can come in direct contact with, or even grow into the myometrium, which leads to placenta accreta.

And this can occurs typically when the placenta implants at a site of damaged endometrium.

One of the most common causes of damaged endometrium these days is a cesarean section scar.

So if you have a placenta that comes down over a cesarean section scar, it can, that placenta can touch the myometrium or even grow into it.

And the complications of placenta accreta and the other family members, accreta or percreta, are difficulty removing the placenta after delivery, such that tugging on that placenta may tear it and cause dangerous bleeding to the mother.

There can also be bleeding at delivery, which can be so heavy as to necessitate hysterectomy.

Also, with an increta or percreta, that area of the uterine wall is weakened by the placenta growing in, which can lead to uterine rupture, or you can have internal hemorrhage with a percreta.

In a woman who's had one or more prior c-sections in the past, and now she's pregnant again, and in her current pregnancy, the placenta lies over the scar, which usually happens with an anterior placenta previa.

Then the woman is at a substantially increased risk of an accreta increta or a percreta if the placenta lies over the area of a prior C-section scar.

If a woman has had one prior C-section and the placenta implants over that area, she has a one in four chance, 24% chance of having a placenta accreta.

If she's had two or more prior C-sections, and the placenta implants over that area, over the lower uterine segment scar, she has a almost 50% chance of having an accreta.

So anytime you see a woman with an anterior placenta previa or a low lying placenta in a woman with prior cesarean sections, you should always raise the question or the possibility of a placenta accreta.

That's regardless of what the ultrasound shows other than a previa or low lying placenta, just the fact that it overlies the scar means that if she's had a prior C-section, means that she has good chance of having an accreta.

If you see that, namely the placenta overlays the region of the scar in a woman of prior c-sections.

And on top of that, the myometrium looks very thin over the placenta, or there's no myometrium seen over the placenta.

That indicates an almost certain placenta accreta.

And if the placenta extends through the uterine wall, for example, into the bladder, then you've diagnosed a placenta percreta.

Another finding that often goes along with an accreta and increta or percreta are large irregular placental venous lakes.

So if you're thinking about the diagnosis, that should help you be more certain.

Here's an example of a placenta accreta.

Here is the placenta, and at least in this region, we see no myometrium around it.

And you can also see that there are large irregular venous lakes in the placenta, some of which fill in with color doppler.

So this is a placenta accreta, at least an accreta.

And this woman ended up having a hysterectomy during delivery to control her bleeding.

And pathologic examination confirmed the diagnosis of a placenta accreta.

Here's a percreta where the, this is a sagittal view, that's the fetal, that's the mother's bladder.

And here is the uterus, and you can see here, here is the placenta.

You can see the placenta is growing all the way through the wall, and looks like placental tissue is coming into contact with urine and the mother's bladder.

And that was confirmed at pathology.

Accreta don't have to happen and don't always happen, or don't only happen in the lower uterine segment at c-section scars.

They can occur anywhere in some cases.

Here is a case of a woman who had a prior D&C, which presumably damaged her endometrium, which led to a placenta accreta in the fundus.

For normal comparison.

You can see here is the placenta, somewhat calcified placenta.

And here is the hypoechoic myometrium overlying it in distinction, this case also up in the fundus, there's the placenta, but at a part of the placenta, you see no overlying myometrium, no myometrium between the placenta and the bright echogenic tissue outside the uterus.

So this is a placenta accreta or worse in a woman who has her accreta, not at the lower segment.

Placental Chorioangioma

Placental chorioangiomas occur in about a half to 1% when the placenta is looked at pathologically, it's a benign tumor, benign, quite vascular tumor of the placenta.

We often don't see them, especially late in pregnancy because the placenta is heterogeneous.

If it's heterogeneous, the chorioangioma may not stand out that clearly.

But if it's earlier in pregnancy and a chorioangioma is there, as we'll see in a minute, they can be quite, they're usually quite easy to see.

Most of them have no clinical significance.

Occasionally, if they are larger or have very high blood flow, you can have complications including polyhydramnios, thrombocytopenia, hemolytic anemia, and intrauterine growth restriction.

And here's an example of a placental chorioangioma.

The placenta is mostly quite homogeneous, but there's a focal hypoechoic area right here that has quite a lot of blood flow on the colored Doppler view.

This is a chorioangioma, as I mentioned, they usually are cause no problems, but when they're big, and here's another chorioangioma, there's the end of the placenta.

Large chorioangioma fire amount of blood flow, they can lead to fetal hydrops in some cases.

And here we see the early phase of hydrops, which is a dilated umbilical vein.

And this is due to vascular steal phenomenon through the chorioangioma.

The Umbilical Cord

Okay, let's move from the placenta to the umbilical cord.

Here's a nice 3D view of a fetus at about 12 weeks where we can see the cord looping away from the baby at the umbilicus in here to the edge of the uterus, actually at the placenta.

And here's a color 2D video clip of the placenta with the two umbilical arteries.

There are a number of abnormalities that we can see in the umbilical cord.

I'll be talking about some of them, but not all of them here because of time limitations.

One of the key ones is to determine the structure of the cord.

The normal structure of the cord is that normal, it has three vessels, one vein and two umbilical arteries, one umbilical vein, two umbilical arteries.

The difference in appearance is that the vein is big and the in cross-section, the artery is small.

And we can see that on the normal case here, where you see a loop of cords surrounded by fluid.

This larger black areas the umbilical vein, two smaller black areas are the two umbilical arteries in cross section.

We can see it by turning color doppler on the arteries, the two arteries in the vein, but not necessary.

To see it.

We can see it perfectly well in the 2D.

This in distinction is the as an abnormal two vessel cord or a single umbilical artery.

There's one vein, one artery instead of one vein, two arteries.

This is an abnormal cord, also confirmed by a color doppler where you see the vein.

And one artery.

If you can't isolate a loop of cord to get a good cross-section of it.

And as I showed on the prior slide, you can get another way.

There's another way of telling whether there's one umbilical artery or two umbilical arteries.

And that is to do use color doppler through the fetal pelvis.

Here, fetal pelvis, there's the fetal bladder.

And you can see by color doppler two arteries.

This is normal.

So it's a two umbilical artery or three vessel cord.

Three VC is three vessel cord.

Here.

On the other hand, there's the bladder.

And with color doppler, there is one umbilical artery, but not on the other side.

This is a single umbilical artery or a two vessel cord.

Now, why is it important to know if there's a two vessel cord instead of a three?

Well, this abnormality, which occurs in up to 1% of singletons and quite a bit more commonly in twins, is important only because there is a fairly high chance and a fetus with a single umbilical artery, that that fetus has structural anomalies or aneuploidy abnormal chromosomes up to about 30%.

So when you see a single umbilical cord, it's important to take a very, very, very careful look at the rest of the baby.

Umbilical cord cysts can be seen in any trimester, first, second, third, they usually cause no problems.

But there have been associated or reported association of umbilical cord cyst with fetal anomalies, including anencephaly, cardiac or renal anomalies.

And they've been associated with aneuploidy.

Here are a few examples.

First trimester, there is the head and body of the fetus, bit of the umbilical cord, and there's a cyst in part of the cord.

Here is another case.

This is in the late second trimester.

And what we're seeing is there's the fetal abdomen that's actually the fetal bladder.

You can see a little bit of normal cord.

And then this part of the cord here, there are two big cysts.

There's one, there's the other, and color doppler.

The cord vessels light up the cyst do not.

Umbilical cord varix is a focal dilatation the umbilical cord that can occur within fetal abdomen or in the umbilical cord, usually in the fetal abdomen.

And it also has been associated with an elevated risk of structural anomalies.

An and other problems including fetal demise, possibly because the blood flowing flows slowly in the varix, in the dilated vein and may thrombose.

And here's an example of an umbilical vein varix.

The umbilical vein is normal here, then it balloons way out, and then it's normal again.

And here you can see on color doppler that it lights up with color.

The another ultrasound feature of the umbilical cord is where the cord inserts into the placenta.

Normally, the cord inserts, if this is the placenta, and this is the umbilical cord, normally it inserts somewhere at or around the middle of the placenta.

If it occurs at the edge of the placenta, it is a marginal insertion.

And if instead of coming out into the amniotic fluid, as soon as it leaves the placenta, if it travels under the membranes for a while, and then only later after traveling through the membranes for a while, comes into the amniotic fluid.

That's called velamentous cord insertion, or sometimes termed a membranous cord insertion.

And with these, these are also associated with an elevated risk of problems, probably or it's thought to be because this the umbilical cord normally is in the amniotic fluid.

And when it travels through the amniotic fluid, it's protected by what's called Wharton's jelly.

That's part of the cord that's under the membranes is not protected by Wharton's jelly, and it's thought to be a greater risk for compression or rupture.

And here are examples.

This is the normal cord insertion coming from around the middle of the placenta.

Here's the placenta in back, and this is the edge of it, or the margin of it.

And the cord is coming off right at the margins, the marginal cord insertion.

And here's a velamentous cord insertion.

The placenta comes, the cord comes off somewhere around here, but then instead of going right into the amniotic fluid, it travels under the membranes.

And then only later does it come into the amniotic fluid.

This part is at risk for rupture or compression with a velamentous cord insertion.

If the, since the membrane travels, for the cord travels for a while under the membranes away from the placenta, if it happens to during its course under the membranes go over the cervix, it's called a vasa previa.

You can also get a vasa previa when there are two lobes of the placenta and the part of the blood vessels that connect them.

If that travels over the cervix, that's a vasa previa.

With a vasa previa, it can have very serious complications.

The if a vaginal delivery is attempted, the vessels can tear during delivery, which could lead to fetal hemorrhage.

And in severe cases, fetal exsanguination and death, we make the ultrasound diagnosis.

When we see a vessel over the cervix that is fetal, it has a fetal heart rate as opposed to maternal heart rate.

And if you're not sure whether it's held there under the membranes or it just happens to be lying there, sitting there during the time, repeat the ultrasound a few minutes later or if necessary at a later date.

And here's an example of vasa previa.

There's a placenta core, the cord coming off and then going under the membrane.

So it's a velamentous cord insertion and then extends right over the cervix.

That's a vasa previa.

The final abnormalities that we can diagnose by ultrasound, it's important to recognize them if they're there, are umbilical cord presentation and umbilical cord prolapse.

Cord presentation is when there's a loop of cord that lies below the presenting part of the fetus in the presence of intact membranes.

And cord prolapse, which is much more important, is when the umbilical cord protrudes through ruptured membranes into the vagina, usually during labor, and that can lead to fetal hypoxia and fetal morbidity and mortality.

And here's a case of prolapsed cord.

You can see that there's fluid extending through an open cervix here and into the vagina.

And the cord is coming through this area.

So it's prolapse of the umbilical cord.

Amniotic Fluid

The last thing that I'll talk about is ultrasound of amniotic fluid.

Here the questions are, are there too much, too little, or is it too bright?

Amniotic fluid, it's important to know a little bit about the source and the regulation of amniotic fluid.

Up to about 16 weeks.

Amniotic fluid occurs as a result of diffusion of fluid through the membranes, the placenta, the umbilical cord, and the fetal skin.

That's early in pregnancy.

But from 16 weeks onward, the amniotic fluid is produced largely by fetal urination and consumed by fetal swallowing and gi tract absorption.

Also to some extent by lung absorption.

The reason this is worth knowing is that if there's a production problem fetal urine isn't being produced, or there's obstruction, bilateral obstruction to blood flow, if there's a production problem, you'll have oligohydramnios.

If there's a consumption problem, such as with esophageal atresia where the baby can't swallow the fluid and therefore consume it in its gi tract.

There will be polyhydramnios pictorially.

Amniotic fluid is produced by fetal urination.

There's a boy and a girl peeing.

And here is consumption is by swallowing and getting the fluid down into the GI tract.

If we ever wanted to know amniotic fluid volume, we can't tell it directly by ultrasound.

The method to determine amniotic fluid volume accurately, in fact, is by a method called dye dilution.

What we do, what we could do for this, and we rarely do it, there's rarely a reason to do it, but if you had to know how many ccs of fluid there is in the bag in the pregnancy, what you would do would be to inject some concentrated dye, put a needle into the fluid, inject some dye, and then wait a few minutes as the mother rolls around or walks around, let the dye distribute itself evenly through the amniotic fluid, then put a needle back in and take a little out and see how much it's been diluted.

If you put in one cc or one milliliter, and then the next time you stick the needle in a few minutes later, it's diluted that one a thousand fold, then the fact that one milliliter got diluted a thousand fold means that there's a thousand milliliters or a thousand ccs in of amniotic fluid.

That's the only way to get actual numbers or actual volumes of fluid.

And people have done such studies with dye dilution to get the actual median or average amniotic fluid volume at different stages of pregnancy.

It it's maximum in the late third trimester where it hits almost a thousand ccs median and then begins to drop off a little bit amniotic fluid in the first trimester.

The it's important to know what it looks like and how much there is normally in the early first trimester, there is little or no amniotic fluid because the amnion is closely applied to the embryo itself.

This little yellow area, maybe a little amniotic fluid most is this green chorionic fluid between the amnion and the chorion.

By the mid to late first trimester, you can see about equal amounts of amniotic fluid, which is yellow here, and chorionic fluid.

And then by the end of the first trimester or early second trimester, the fluid is virtually all amniotic fluid.

And here's a progression.

At six weeks, you can see the yolk sac, the embryo, but no amnion is seen because it's right up against the baby.

So there's no amniotic fluid.

All this fluid is chorionic fluid at seven weeks.

A little amniotic fluid, a lot of chorionic fluid at eight weeks, a little more amniotic fluid.

More at 9, 10, 11 by 12 weeks.

It's almost completely almost all the fluid is amniotic fluid 'cause the amnion is almost up against the chorion.

And generally by the end of the first trimester or beginning of the second, all this chorionic fluid's gone and all the fluid you see is amniotic in the second and third trimesters.

There are two features of the amniotic fluid that are relevant.

One is its echogenicity or brightness, and the other is the amniotic fluid volume.

I'll talk about both of those before ending.

Echogenic Amniotic Fluid

Let's first talk about bright amniotic fluid.

There are a few different etiologies or causes of bright amniotic fluid.

One which is common is physiologic etiology.

Vernix, which are the little white flakes that you see on a baby's skin after it's born.

Those little flakes break off and float around in the amniotic fluid causing bright reflectors and bright amniotic fluid.

That's physiologic non-pathological.

They're also a number of pathologic causes of echogenic amniotic fluid, including blood meconium or squames and fluid as with chorioamnionitis.

So the key question to address is, should we ever worry when we see echogenic amniotic fluid?

Well in the third trimester?

So here's a report of a couple of studies or results of a couple of studies that have been done in the third trimester.

Echogenic fluid is due to vernix in well over 90% of cases.

So whenever you see bright fluid in the third trimester, you should always assume it's vernix.

Unless there's a very strong clinical suspicion of blood meconium or infection in the second trimester, you have to strongly consider a pathologic cause, especially if the fluid is very echogenic.

So just examples here are two different second trimester pregnancies with echogenic amniotic fluid.

Here are actually twins at 21 weeks, the one you can see normal fluid and bright fluid.

This woman was having fever and pain clinically suspected of having chorioamnionitis.

And we did an amniocentesis, but we were pretty sure that was going to turn out to be infected.

And sure enough, it came out with a lot of pus.

Here is another case of echogenic amniotic fluid here at 18 weeks, and this is blood in the amniotic fluid.

On the other hand, these are two third trimester fetuses at 25 weeks at 37 weeks.

In both cases, you see small, bright particles floating around in the fluid.

In both of these cases, we would assume it to be vernix, unless there's a strong clinical suspicion that it might be blood meconium or infection.

But in the absence of that clinical suspicion, we would just say it's vernix, it's normal.

Amniotic Fluid Volume Assessment

The last thing I'll talk about is assessing amniotic fluid volume in the second and third trimester.

And here what we're trying to do is not get the exact volume of the fluid, but categorize it as polyhydramnios or oligohydramnios or normal.

This is a case of polyhydramnios.

Here's a case of oligohydramnios.

How do we characterize it?

According to the guidelines of the American Institute of Ultrasound in medicine for second and third trimester obstetrical ultrasound, and similarly for American College of Radiology or American College of Obstetrics and Gynecology Guidelines, they state that a qualitative or semi-quantitative estimate of amniotic fluid volume should be reported.

And they're saying that it's acceptable to use either qualitative estimate or semi-quantitative estimates, such as the amniotic fluid index, single deepest pocket or two diameter pocket.

These such as the amniotic fluid index, are semi-quantitative.

The only real quantitative method would be the dilution method I mentioned earlier, which are not done on any regular basis in ultrasound.

So the sonographic assessment can use subjective assessment, single deepest pocket measurement, or the amniotic fluid index, which is the sum of the deepest pocket in the four quadrants.

Single deepest pocket is considered to be oligohydramnios if it's less than one or two centimeters and polyhydramnios of greater than eight, the amniotic fluid index and approximately less than five centimeters is oligo greater than 18 to 20 is polyhydramnios.

Here is case two different cases.

Normal of normal amniotic fluid volume we're sweeping through.

And so this is, it looks subjectively normal.

And when we do an amniotic fluid index on a normal case, we're getting 12.4 millimeters.

Here subjectively, there's very little fluid as we sweep through.

And here you can, that's confirmed by an amniotic fluid index of 4.2, less than five, which is oligohydramnios.

And here's case of polyhydramnios.

When we sweep through, especially towards the end of the sweep, before it re you see more fluid than you would expect at 30 weeks.

And the amniotic fluid index is also elevated.

So what are the which one should you use?

Subjective assessment is quick and efficient accounts for gestational age variations.

The only potential downside is it may be of questionable reliability with an experienced operator.

It is best documented as I showed you in the prior slides with a video clip.

The single deepest pocket or amniotic fluid index is simple and quick, especially the single deepest, but even the amniotic fluid index is pretty simple and quick.

But these have a number.

These are the semi-quantitative methods.

They have a number of problems.

Even with oligohydramnios, you can have one or more deep pockets that don't have much fluid in them, such as in crevices in the fetal neck or between the fetal legs.

The amniotic fluid index can be affected by fetal movement from one quadrant to another.

And another problem with these semi-quantitative methods, they're not really mathematically valid.

Linear measurements do not correlate with volume, and this is a schematic indicator of why that's true.

Here are two different pictures or diagrams of two different people.

They have the same linear measurement if you measure height, but they have very different volumes.

So linear measurements do not correlate with volume.

So which method should you use?

Well, there have been a couple of published studies that have used dye dilution as the gold standard and then comparing the gold standard to subjective assessment or amniotic fluid index.

And what these studies have found is that there's really no significant difference between subjective assessment and amniotic fluid index when you compare it to the gold standard.

So either of them are about as good as the other, but unfortunately neither of them is terribly accurate at diagnosing elevated or decreased fluid volume.

So they're not great, but they're all we have.

So you should always assess fluid, and you can either use subjective assessment and amniotic fluid index.

Either one of them is acceptable.

Conclusion

So I've come to the end of the tour of amniotic fluid volume, as well as the placenta and umbilical cord.

I hope you found it useful and educational.

Thank you.

Bye-bye.