The Masters Lecture Series

Introduction to Sonography of Multiple Gestations

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

And I'll be speaking on sonography of multiple gestations.

I'll spend the next 45 minutes talking about the ultrasound of multiple gestations.

Ultrasound of multiple gestations is, I find a very interesting topic and a very interesting part of ultrasound to do because, when there are twins or even higher order multiples, doing ultrasound involves looking, doing everything you do for a single gestation, doing it multiple times.

For example, when you're looking at twins, you have to look over both fetuses in the same way that you would look over each fetus in a, or at least fetus in a singleton gestation, as well as the placenta cord.

So you have to repeat that multiple times.

But what makes it even more interesting is that, there are additional things to look for the kinds of abnormalities that occur only in twins, or higher order multiples.

And those are some of the things that I'll be focusing on here.

Problem Case: Early Multiple Gestation

Before we go any further, I'll pose a little, problem case, and the answer will come up in a few minutes.

But, looking at this, this is a transvaginal closeup view of a multiple gestation at about five and a half weeks.

And the question is, what type of multiple gestation is it?

What you can see on the image are two gestational sacks, each with one yolk sack.

So are these dichorionic diamniotic twins?

Are they monochorionic diamniotic twins, or are they something else, or you just can't tell?

So, keep this in mind.

Think about it, and we'll see the answer very shortly.

Lecture Outline

So, the outline of my lectures as follows.

I'm gonna talk about some general information, including information about, incidents, of multiple gestations place presentation type, which refers to the chorionicity and the amnionicity of a multiple gestation.

And, a little bit of background about morbidity and mortality.

And then I'll spend most of my time talking about ultrasound of multiple gestations in a number of, categories.

General Background on Multiple Gestations

So, let's do some, non ultrasound background.

Look at multiple gestations.

Um, so one feature of any multiple gestation, and let's focus on twins for the moment.

One feature is zygosity.

Twins can either be monozygotic or dizygotic monozygotic.

Twins are also called identical twins.

And, dizygotic twins are also called fraternal twins.

Monozygotic twins occur from a single sperm, fertilizing a single egg.

And what happens is it becomes a fertilized, a single fertilized egg or a zygote.

There's only one of them. So they're called monozygotic.

That twin, sorry, that fertilized egg splits and into multiple cells.

And then at some point, after the beginning, splitting occurs into two bundles of cells, and each one of those leads to a baby, ideally with dizygotic or fraternal twins.

You start out with two eggs, two sperm, one sperm, fertilizing each egg.

You end up with two fertilized eggs, or two zygotes, which is why they're called dizygotic.

And, they, each one leads to a bundle of cells and ultimately to a baby.

That is one feature of twins, the zygosity.

Placentation in Twins

Another important feature is the placentation of twins, whether they're monozygotic or dizygotic.

And, this is, not the same as, sorry, the placentation refers to whether they're monochorionic dichorionic, monoamniotic, diamniotic placentation has a relationship to zygosity, but it is different.

So from Zygosity.

So let's take a look at identical or monozygotic twins.

The, placentation type depends on when the splitting occurs.

The earlier the split, the earlier the splitting occurs, the more separate the membranes.

So when the splitting occurs between zero and four days, which is, corresponds to when they're in the tube in the, fallopian tube, this splitting.

If the splitting occurs in the fallopian tube, before the bundles of cells reach the placenta, they're gonna have completely separate membranes.

They're dichorionic diamniotic, or as we call them for short di di twins.

About one third of identical twins or monozygotic twins are di di.

Two thirds of the time.

The splitting occurs later between four and eight days, which is in the first few days within the uterus.

And when that happens, the twins are monochorionic, they share a chorion.

And since the placenta is part of the chorion, it's a thick part of the chorion.

If they're monochorionic, they have one chorion, one placenta.

But, these twins that split between four and eight days are gonna be diamniotic.

So they're monochorionic diamniotic.

Um, and about two thirds of identical twins are monodi.

Two thirds of them split between four and eight days.

The very late splitters, after eight days, and this is quite rare, not only share a chorion, they're monochorionic, but they're also share an amnion.

They're monoamniotic.

And as we'll see at the end of the talk, the very, very late splitters are not only mono mono, but they may be conjoined.

Okay? So that is the story for monozygotic. Identical twins.

A third of them are di di.

Two thirds of them are mono di, and one, about 1% are mono mono.

Now, what about fraternal or dizygotic twins?

Well, all of them split right from the get go.

All of them are like the zero to the zero day splitters of the, identical twins.

So they are a hundred percent of the time di di.

All fraternal twins are dichorionic diamniotic.

Using Zygosity and Placentation in Ultrasound

So what can, how can we use this information when we're doing ultrasound?

Well, in a, in a couple of ways.

One is, let's say we're doing ultrasound, 20 week twins.

We've never seen them before. And we see a boy and a girl.

If we see a boy and a girl, they have to be identical or fraternal.

They can't be sorry if they're a boy and a girl.

They have to be fraternal. They can't be identical.

If they're fraternal, they have to be di di.

So if you see a boy and a girl, you don't need to look at anything else.

They have to be di di.

Um, so you know, that's one of the, pieces of information from this chart that is relevant, to us in ultrasound.

What's another relevant piece of information?

Let's say you're doing an ultrasound and you see twins and you decide using the kinds of criteria that I'll be talking about soon you decide, they're, you determine that they're monochorionic.

Let's say they're mono. You see twins at six weeks, and they're mono di twins, as you can see from this chart.

If they're mono di, they have to be identical because they can't be fraternal and be mono di.

So if you do an ultrasound six weeks, seven weeks, 10 weeks, 15 weeks, anytime, and you determine that the twins are monochorionic, you have immediately determined that they have to be identical.

So you can tell the mother or the parents, congratulations, you only have twins, but we can tell you that they're identical.

Complications of Multiple Gestations

So what are the, some of the complications of multiple gestations?

The complications relate directly to the placentation type, to the chorionicity and amnionicity, and the general rule is the more separate the membranes, the fewer the complications.

So the most separate the membranes can be with twins is if they have two chorions and two amnions, no, sharing of membranes, they're di di.

These twins are at risk for premature delivery and low birth weight.

These, of course, premature and delivery and low birth weight are complications that can affect, any pregnancy.

But they're more common among twins than singletons.

If the twins share a chorion, which means they share a placenta, they're monochorionic, but they don't share an amnion, they have separate amnion.

So they're monochorionic di amniotic, they have the potential complications of premature delivery in low birth weight, but in addition, they're at risk for two abnormalities that are related to sharing a placenta, the fact they're monochorionic, twin, twin transfusion syndrome, and a cardiac anomaly.

And finally, for the rare situation when they're not only she a chorion, they're monochorionic, but they share an amnion, they're monoamniotic, they have all these four risks plus two additional ones, cord entanglement and conjoined.

So we're gonna talk about the, as we get into ultrasound, we're gonna talk about diagnosing chorionicity and diagnosing some of the complications.

Ultrasound Assessment: Determining Pregnancy Number

So let's move on to ultrasound.

Now, the first most basic thing we do on ultrasound when multiple gestations is determine, or with any pregnancy, is to determine pregnancy number.

Is it single 10 twin triplet?

And you might say, well, why Is there anything to talk about here?

Don't we just count the number of fetuses or embryos that we see?

And that's the pregnancy number.

Well, that's true only after about six weeks when we start seeing the embryo or fetus prior to six weeks.

It's a little more complicated than that.

So in terms of the assessment of pregnancy number on ultrasound after visualization of, of the embryo at about six weeks, again, it is simple.

We count the embryos or fetuses with heartbeats, but prior to six weeks, we don't have that, quite so accurate a rule.

And what we can do is count gestational sacks and yolk sacks.

And that gives us some clue, but not a definitive answer as we'll see, the potential problems early on are that we can over count one of the, if you have twins or triplets or any multiple early on, there's no guarantee that each one is gonna make it.

One of them may, not infrequent that one of them will die.

And, and, so-called vanish, it will resorb and not ever be seen again.

More interestingly, it's not uncommon to under count twins prior to six weeks or under count multiples prior to six weeks.

And I'll show you several examples.

And, it happens surprisingly often.

And we've called this the so-called appearing twin phenomenon.

Okay, so let's, take a look.

Here are is a five week scan.

We take a look, it's transvaginal scan.

We're seeing two fluid collections surrounded by a bright ring.

These are two gestational sacks.

So we can tell the parents that, as far as we can tell, she's having twins, we can't be sure that they'll make it.

We can't be sure there won't be a vanishing twin.

And one, or even both of them will fail to grow, as we'll see later.

We also can't be sure that there aren't gonna be more than two.

But our best estimate and a pretty reliable estimate is that this woman is gonna have twins.

'cause we see two gestational sex, at a few days later on another case, these are also twins.

There's a single gestational sack.

But the reason we know that they're twins is they're two yolk sacks within it.

So usually there's a fetus for each gestational sack usually.

So our best estimate is that these are gonna be twins.

We could be wrong, but as we'll see.

But, these are best estimate as twins.

And then finally, once we are at, beyond six weeks and we see the embryo and the heartbeat, then it's easy.

Then, we count embr.

Here's three embryos, all with heartbeats.

These are triplets. No mystery there.

The Appearing Twin Phenomenon

So the appearing twin phenomenon is, occurs again prior to six weeks when ultrasound may under count pregnancy number, which can lead to a so-called appearing twin on a subsequent scan.

This can be kind of, embarrassing.

If you don't recognize and explain to the patient that this can be can happen, it can be embarrassing.

If you do a scan at five or five and a half weeks, you tell the woman, you're having a singleton pre, I see a singleton pregnancy.

She comes back at some point in the future, and to your surprise and hers, there are twins kind of embarrassing.

And she may think that you made a big error on the first scan, not seeing one.

Or you might see, say, congratulations, I see twins.

And then she'll come back with a third as you.

And you'll see these kinds of things over the next several slides here.

Uh, here's an example.

At about five weeks, five to five and a half weeks, we do a scan.

That's a transvaginal scan. We see a single gestational sac.

Tell the woman, congratulations, you're pregnant.

We see, we see a, pregnancy in there, a gestational sac looks like a singleton.

Comes back a week and a half later and whoops, a little embarrassing.

There's now two of them. They both had heartbeats.

This one is smaller.

And that may be why we didn't see it here.

It may have been too small to see, but usually in these cases, the smaller one catches up.

And, there's no continuing discrepancy.

These are undercount twins.

Early on, here's another case where at five week, five and a half weeks, we say we see a gestational sack.

We see a yolk sack.

Looks like you have a nice normal, as far as we can tell.

Normal singleton pregnancy comes back a few weeks later.

And lo and behold, there are actually twins.

There's one twin, the other within a single gestational sect, there are also under counted or appearing twin.

There's another case, five and a half weeks, two gestational sax scene, seven weeks, three weeks, a week and a half later.

Again, whoops, there aren't two, there's three.

So these kinds of appearing twins are appearing fetuses are not that uncommon.

Let's take a look at this.

This is the case that I showed right at the beginning as a little problem case.

Are these di di twins, mono di twins, or you just can't tell?

Well, because there's a thick separator between them.

They're certainly not mono di twins.

So we can eliminate that In all likelihood, the best guess is that they're di di twins.

But if the mother said to you, how can you be sure that there aren't two fetuses in here, or two fetuses in here?

How do you know it's not more? The answer is you really can't tell.

And in fact, when she did come back a few weeks later, she did have triplets.

And so one of these gestational sacs has one fetus.

The other developing though, too small to see, the other one has mono mono twins.

As you can see here. These are mono mono twins in one of these sacs.

And here are 10 weeks, you see them even more clearly.

So the answer, these were under counted triplets reported first as twins.

Um, so how, you know, we did a, we did and published a study a number of years ago where we looked at all cases where we could potentially under count early.

In other words, women who had early scans prior to six weeks and then on a follow-up scan actually had a multiple.

So we looked at how often we actually we under counted versus how often we correctly counted on the original scan, there were 325 cases that had early scans followed by a multiple.

And who are amazement When we were, when we did a search of our database, we found 47 cases in which outta those 325 that were in, which, the multiple gestation was counted on the five to 5.9 week scan under count rate of 14%.

So if there are multiples, you may not know it on the first scan, you have a 14% chance of undercounting it.

So how do you avoid the embarrassment of, in these 14% of cases, having the woman come back with more than you told her the first time?

Well, the answer is that when you do a five to 5.9 week scan, it's what you should tell the patient is, as far as I can tell, you, have a single open pregnancy.

But ultrasound can miss early pregnancies.

You may have fewer on a followup scan if there's a vanishing twin.

You may have more if there's an appearing twin.

Similarly, if you see two, you can say, I think there's two, but it's possible on a followup, you'll have fewer.

It's possible you'll have more if you warn patients on the five to five point week, 5, 9, 5 to 5.9 week scan that your number is just an estimate, and that the number can go up or down.

You'll save yourself the embarrassment, if the number does go up or down on subsequent scans.

Assessment of Placentation Type: Chorionicity and Amnionicity

So let's now move to another important area of ultrasound of multiple gestations, namely assessment of placentation type, chorionicity and amnionicity.

One important statement that I would make here is that every single report of a multiple gestation ultrasound should include a statement about placentation type.

Should have a statement such as dichorionic diamniotic twins, mono di twins, diamniotic, probably dichorionic twins, triamniotic, trichorionic, twins, whatever.

If you ever see a report of a multiple gestation that doesn't have an assessment of chorionicity and amnionicity, it's an incomplete report.

So how do we tell the difference?

Well, schematically, these three diagrams show di di twins on the left mono di, twins in the middle and mono mono twins at the end di di twins.

You can see if you look at the intertwine membrane, what does it consist of?

It has an amnion layer here.

Here's a, the chorionic membrane of this twin here.

Note that the placenta is the thick part of the chorion.

The chorionic membrane is the thin part of the membrane.

The inter twin membrane then goes on to have the chorion of the other twin here and the amnion of the other twin here.

So the inter twin membrane with di di twins has four layers, two amnions, two chorions.

In distinction, the mono di twins have one placenta, one chorion going all the way around that chorion is not part of the inter twin membrane.

So the inter twin membrane consists solely of two layers of thin amnion.

So these are much thinner than these.

The monodi membranes are much thinner than the di di membranes.

With mono mono twins, we can only tell their mono mono as we'll see in a minute, if you not only fail to see a membrane between them, but the cords are intermingled.

If you don't see intermingling of the cords and there's only failure to see a membrane, you never know whether the membrane is there or not, visible or not there.

Um, only if you see intermingling of the cords can you know that it's really not there.

So thick membrane di di, thin membrane mono di, no membrane seen and intermingling of the chords.

Mono mono, these rules are not bad, but they as we'll see, they don't always work.

For example, it isn't always so easy to tell the difference between di di twins and, membrane of mono di twins.

They're both fairly thin in the second and third trimester.

So here are di di twins.

At five weeks, there's two separate gestational sacs separated by thick band of tissue.

These are, di di twins.

Again, it's possible that there's even more, there could be an appearing triplet, but two are best, best guess.

These are twins. And if they're twins, they're di di, di di twins.

Here on a 3D view at, 10 weeks, again, you can see fairly thick membrane, not the very thin wispy membrane of a, monodi twins.

On the other hand, here is that wispy membrane of monodi twins that corresponds that, consists of two layers of amnion only.

No chorion very thin, in other words.

And here are mono mono twins, the rare ones in the, first trimester.

We know they're mono mono, partly because we see, a single amnion all the way around them.

And as additional information as we sweep through the pregnancy, there's only one yolk sack seen.

Now, since, the number of amnions is almost always equal to the number of yolk sacks, since we see one yolk sack, it means there's one amnion, triplets, and higher order multiples can have different combinations of chorionicity and amnionicity.

Here are, triplets that are triamniotic because each one is separated from the other by a membrane that consists, contains at least amnion.

But, we have one thick membrane and one thin membrane.

So this fetus separated from the others by a thick membrane, has its own chorion, its own placenta.

These two twins, which have a thin membrane between them are monochorionic, and diamniotic.

So monochorionic for this, plus monochorionic for that singleton adds up to two chorions, but three amnions.

So they're dichorionic, triamniotic.

Second and Third Trimester Assessment

Um, in the second and third trimester, the we use different, approaches to diagnosing chorionicity and amnionicity or somewhat different approaches.

Here, the membrane, we can't use membrane thickness, or it's the last thing we want to use if nothing else is available.

These two twins are di di.

We know they're di di by counting placenta.

This placenta with this one, this placenta, with this one.

So regardless of how thick or thin the membrane looks, these are di di twins.

Here's another case where we use information to determine these are di di.

Here's, here's a male and a female.

Um, and, male and a female have to be fraternal.

They can't be identical.

Fraternal twins, as we saw on an earlier slide, are always di di.

If you see a boy and a girl, it doesn't matter what else you see, they're di di.

Some of the problems that we have, in, determining chorionicity include, if you see monochorionic twins, twins in one gestational sac prior to six weeks, how do you determine monoamniotic versus diamniotic twins?

The problem is, the amnion is not generally visible prior to about six or seven weeks, usually prior to seven weeks.

So if you can't count amnion, how do you, if you can't see them, you can't count them to determine the amnionicity.

So a challenge is to determine monoamniotic from diamniotic twins if they're monochorionic in the early first trimester.

The amnion, as I mentioned, is not generally visible prior to seven weeks with a single and pregnancy, you will see yolk sac and an embryo, but no amnion.

So if you see yolk sac embryo yolk sac amnio, but no amnion, how do you count to amnion?

How do you know if they're have a single amnion mono amniotic or two amnions diamniotic?

Well, the answer is that to determine the amnionicity count, the yolk sacks, the number of amnions is almost always equal to the number of yolk sacks.

So if you see one yolk sack, they're monoamniotic, two yolk sacks, they're diamniotic.

Here are monochorionic twins.

You can see one gestational sac, two yolk sacks, two embryos, two heartbeats.

These, even though you don't see any amnions here, you can't see the amnion necess early on.

Um, you can say with almost complete certainty, these are di amniotic twins.

They're monochorionic for sure, because there's one gestational sac.

But the fact that we see two amnions means that they're probably di uh, two yolk sacs means that they're probably di amniotic.

So this should be reported as monochorionic, probably diamniotic twins.

And notice that, when she came back for ultrasound a few weeks later, it confirmed that there's diamniotic, there's the, membrane separating the two twins, in, with monochorionic twins after the, early first, trimester.

It can, be challenging to distinguish mono, from diamniotic twins.

Um, since you don't always see a membrane when it, if a thin inner twin membrane, if you don't see it, how do you know if it's there or not?

If you don't see it, it's not enough.

Failure to visualize a membrane doesn't prove that it's not there.

You just aren't seeing it. It may be there.

So the challenge is diagnosing monoamniotic twins.

Uh, so how do you tell? Well, you know, they're diamniotic.

If you see an inter twin membrane or different sexes or separate placenta, all these would prove that they're diamniotic, they're monoamniotic.

If none of these apply, and you see intermingling of the umbilical cord or one amnion around two fetuses.

So take a look at this case.

You see br twin one, twin two, no membrane between the two of them based on this image.

You can't tell if they're mono, amniotic, or diamniotic because just because you don't see a membrane doesn't mean it's not there.

But watch what happens when you turn on the color doppler.

When you turn on the color doppler, you can see intermingling of the umbilical cords.

And because they're intermingled, it means that they must be no amnion.

That's the only way the cords can intermingle.

So by turning on the color doppler, we, before this, without the color doppler, we could only say these are monochorionic uncertain amnionicity.

'cause there was no visible membrane.

Now because of intermingling of the membranes, we can say they're mono mono.

Diagnosis of Complications in Multiple Gestations

Okay, let's go on to diagnosis of complications of twins.

There are a number of these complications that are unique to twins, the most common of which is the twin, twin transfusion syndrome.

Twin-Twin Transfusion Syndrome

To diagnose twin, twin transfusion syndrome, we need to, and twin, twin transfusion syndrome is seen in monochorionic twins when there are artery to vein anastomosis between the twin, the twins.

Um, when you have twin twin, when you have monochorionic twins with such anastomosis, you can get unbalanced movement of blood from one twin called the donor twin to the other, the recipient twin.

The way to diagnose twin, twin transfusion syndrome is not usually by seeing these anastomosis.

Usually we don't see them, but seeing three findings.

When we see three findings all together, we can, conclude that there's twin twin transfusion syndrome.

What are the three findings?

Well, as shown schematically, here, we have monochorionic twins.

So you wanna see one placenta, all the findings of monochorionic twins.

You wanna see, another finding is discrepant size, small one and a big one.

And for discrepant size, we use the criterion of a estimate, a difference in estimated weights of at least 25%.

And the other criter in the third criterion is discrepant fluid volumes, low fluid oligo going with the small twin poly with the big twin.

So the ultrasound findings to summarize with twin, twin transfusion syndrome are discordant fetal sizes, a relative difference greater than 25% discrepant amniotic fluid volumes oligo, and the smaller twin sac bali in the larger twin sac and monochorionic placentation.

If you see all these three findings diagnosed twin, twin transfusion syndrome, once you've diagnosed it, they, you can stage it.

There are, proposed staging system from one to five.

The more severe the, the, the higher the stage, the more severe the, twin, twin transfusion syndrome.

The worst of the prognosis.

And these stages can be used and are often used to help guide, decisions about whether or not to treat the fetuses.

So here's a few pictures that I'll follow up with, of twin, twin transfusion syndrome.

Here you can see, a small abdomen, a big abdomen.

When we looked at them quantitatively, there was at least 25% difference in estimated weight.

The fetus with the small abdomen has very little fluid.

This is the membrane that's pretty close to it.

So poly, so oligo had ramoses in the small fetal sac.

All this fluid polyhydramnios is in the big fetal sac.

So there's, and other images prove these to be monochorionic twins.

So there's monochorionic twins with discrepant fluid, poly and oligo and discordant fetal sizes.

This is twin, twin transfusion syndrome.

When the, one of the indications of severe, of a severe twin, twin transfusion syndrome is when there's not only poly and oligo, but the oligohydramnios around the small twin is so, severe that it's a so-called stuck twin.

The membrane holds the baby up against the uterine wall, as in this case, big twin, little twin, lot of fluid.

How do you know whether this fluid belongs to this baby or this baby?

Well, here's the video clip.

Same thing, small one up here, bigger one down here.

We know that this twin is in a funny position.

Normally babies in a pregnancy, sink down to the bottom because they're heavier than the amniotic fluid.

This baby's in a very unusual position. Why is it there?

It's there because the membrane is holding it there.

We can, as we can assume, the membrane must be holding it there.

It's the only reason the baby would be way up there.

So all this fluid belongs to this baby.

So this is twin, twin transfusion syndrome with a stuck twin.

This is a worse prognosis than the garden variety than the typical twin, twin transfusion syndrome.

Another, indication of abnormal, or of bad prognosis with twin, twin transfusion syndrome is when the recipient twin is hydropic, as in this case, small abdomen, big abdomen.

These had all the findings of twin, twin transfusion syndrome.

But on top of that, there was, ascites, or in the larger twin in the recipient twin, this is twin, twin transfusion syndrome with a hydropic recipient, very high risk, situation.

So can we treat this in utero?

Well, remember that, when we're late in pregnancy, you can treat twin twin transfusion syndrome by delivering the pregnancy.

You can eliminate the connection or anastomosis between the two fetuses.

Soon as they come out, there's no longer a vascular connection between them.

When it's earlier, the, there are a couple of treatments that have been, that, are used to improve the prognosis of both fetuses.

One is therapeutic amniocentesis, removing fluid from the larger from the polyhydramnios recipient fetus.

And another is endoscopic laser coagulation of placental anastomotic vessels.

There's a, an extreme treatment that we occasionally have to use to salvage one fetus, and that's if we have twin, twin transfusion syndrome with, one fetus looking like it is about to die, for example, it's not moving and it's bradycardic.

If it dies, then the other, the living fetus as we'll see shortly, is likely to run into a major problem called twin embolization syndrome.

If we do nothing. So if we see twin twin transfusion syndrome, one is about to die, we know that it's gonna take the other one down with it.

Basically, if we don't do anything and what can we do, what we can do for the, to the fetus that's about to die, we can block off or coagulate its umbilical cord, breaking the connection between the two of them.

And here is such an example.

Here I am in the operating room, scanning the baby.

There's the scan.

This is a pediatric surgeon who is working with the coagulation, device or cauterization device.

So this is the baby that looked like it was about to die.

Here we are. But we have blood flow.

We're trying to cauterize the cord of this, this cord.

Here we are, you can see a two-pronged device that we are using that we're trying to snare or capture the cord.

Here. You can see by the way, it the baby moves when we pull the device up and down that we have captured the cord.

And then here you can see right there some bubbles coming up.

And again, there as we, apply an electric current to cauterize the cord, once we cauterize the cord, this baby, this twin that was about to die, will die, but there's no collection connection between it and the other fetus, the living one.

So this one won't take down the other one.

And, right after the procedure, there's severe bradycardia in the one whose cord we cauterized.

And then a day later, that fetus, the heart's no longer beating, and its chambers are full of clotted blood.

So this one died as was going to anyway, but the other one has been protected by the fact that we cauterize this one's cord.

Acardiac Anomaly

Another abnormality unique to twins is the acardiac anomaly.

This occurs as a result of artery to artery and vein to vein anastomosis through the common placenta of a monochorionic gestation.

What happens here is the heart of the, of one of the twins called the pump twin, not only circulates blood around itself, but around the other fetus.

There's two circulations, one around itself.

The other consists of this heart beating.

Blood goes out the artery through the anastomosis in the artery artery anastomosis in the placenta, in the artery of the abnormal twin.

The blood circulates around this twin out its vein through the vein to vein anastomosis in the vein and back to the heart.

So there's a circulatory system here and one here.

Now, this baby cannot survive outside of the utero, has no heart.

And typically as per this diagram, it has an edematous body, often no or a small head in arms.

This ba this, twin won't make it after birth, but, the, if we don't, if we just allow it to continue, the, the, this baby is likely to get into the so-called pump twin severe hemodynamic problems after birth if we suddenly cut the cord, after birth, and we'll see what we can do in a minute.

So with, for an, acardiac anomaly, we make the ultrasound diagnosis when there are monochorionic twins, one with an absent or rudimentary heart.

Doppler shows reverse direction of flow in the umbilical artery and vein in the artery out the vein, as we saw in the prior diagram, which is the opposite or reverse of normal.

And often, the, a cardiac twin is hydropic with an abnormal upper body.

We can treat this by ligation or laser coagulation of the acardiac fetuses umbilical cord.

Uh, note that when we, in, diagnosing an acardiac anomaly, if we have twins, one with a heartbeat and one with no heartbeat, there are two possibilities.

One is that you just have a live twin and a dead twin.

The other is you have a live twin and a, and acardiac twin.

And these are different with respect to their prognosis and what we can do in terms of treatment.

So how do we distinguish if we see twins, one with heartbeat and one without, whether we have a simple live twin, dead twin combo or a live twin, acardiac twin combo?

The answer is by turning on the doppler.

If there's no flow, then it's a live twin, dead twin.

There's no flow in the dead twin.

If there's flow in one of the twins with no heartbeat, it has to come from the other one.

So you have a live twin and a acardiac twin.

And here are a couple of examples.

This is, two side by side views of twins.

This one looks normal. This one is markedly abnormal.

No head, no upper extremities on the 2D view of this fetus.

This is where the head should be, but it's not in the chest.

We saw no heart. There's pleural, effusions and ascites.

So is this a live twin, malformed dead twin?

No, it's not only that. It's an acardiac twin.

This one is the abnormal twin, but there's blood flowing to it and there's no heartbeat.

It has to, this blood flow to this baby has to come from the other twin.

It's an acardiac twin.

Um, here's another case of acardiac twins.

This is a normal looking twin, a very edematous, abnormal looking twin.

Very edematous, no heartbeat seen.

But when we look at the umbilical, artery and vein, we can see them and there's blood flowing towards the fetus.

Reverse direction in the umbilical artery and out the vein.

How did it get here? If there's no heartbeat, it had to come from the other one.

So this is an, acardiac twin confirmed also by the reverse direction of blood flow.

Cord Entanglement

Moving on to another abnormality of twins is cord entanglement.

This is a complication unique to monochorionic twins, and it leads to very high mortality rate in monochorionic.

Twins. Here are monochorionic monoamniotic twins.

Um, and you can see that, they, their cords are entangled.

This is the cord insertion.

They have one common placenta 'cause they're monochorionic, but because they're monoamniotic, the cords wrapped around one another right near the, right near the insertions.

This insertion of one twin's cord into the placenta, the other, but they're entangled shortly after they leave the placenta.

And, and these are at risk for strangulating off, for compressing at the, if, if there's a tight entanglement leading to death of one or both of the twins.

Here again, another set of twins where the cords are not only intermingled, but we see a very unusual appearing configuration.

It looked like a knot.

And after birth, it's confirmed to be a knot.

And yet another case of cord entanglement.

Mono mono twins, one placenta, no membrane, and, separating them.

And here on a, 3D color ultrasound, we can see the cords.

Here's one insertion site at the placenta, the other, and shortly and close to it, the cords and intermingle yet another complication of multiple gestation or conjoined twins.

Conjoined Twins

These are caused by incomplete division of the embryo, usually with very late twinning.

After about 13 days, one can, there are names for types of, conjoined twins like thoracopagus, which are, joined at the thorax.

Lopagus joined at the anterior abdominal walls and others.

But really what we do is not apply names, but, description.

We describe where they're connected, and most importantly, the extent of organ sharing since the prognosis depends on that here.

Conjoined twins diagnosed very early at eight weeks.

You can see twin one, twin two.

There's the head of one, the head of the other two heartbeats.

But right at their pelvises, they are joined to one another.

And that was confirmed a few weeks later.

Common bladder in the joined pelvises of these conjoined twins.

So we sweep through the babies to look for the extent of internal organ sharing.

As we see here, there's separate heads.

The thoraces with the hearts are joined and the abdomens are joined.

Um, we can also, and this is more for the parent's sake, get another view with 3D ultrasound.

Here are the two twins. Same case as this one.

You can see two separate heads.

Their faces are up against one another, separate necks, but then they're joined at the thorax and abdomen.

This one's better for the parents.

Get an idea of what's going on.

This one is better for us in ultrasound because we get a better idea of the extent of internal organ sharing in the thorax and abdomen here than we do there.

We see they're joined on that view, but we can't tell about the internal organs.

And another example of conjoined twins here at the abdomens, the livers are joined the chest.

Were also joined and the faces are partially joined, confirmed after birth.

When you see liver and thorax joined and faces were, faces partly joined.

Twin Embolization Syndrome

Um, the, last abnormality that I'll talk about is something called twin embolization syndrome.

If you have monochorionic twins and one dies for any reason, the survivor is at risk for ischemic damage.

Um, the survivor may develop GI ischemia, janitor urinary ischemia like renal, cortical defects, and most severely central nervous system brain, abnormalities, brain ischemic damage.

I'm sorry. I just wanted to give you, let you know. Yeah.

Um, the risk is greatest if death occurs in one of the twins at about 16 to 20 weeks.

But it can occur at any point if one of mono twin dies in utero for any reason.

And here's, an example of the twin embolization syndrome.

These are monochorionic twins. This one's alive, this one died.

And, the problem is that this one, since it's, it's dead, obviously there's no, it, you know, it's, gone.

But, it took down the other one.

You can see here that the surviving twin, as we go through its brain, this had been normal a few days after the death of the co-twin.

It's just full of cysts. There's no normal appearing brain.

In this one, the brain became ischemic because of the death of the co-twin and twin embolization syndrome.

And this, baby died shortly after birth.

This is another case of twin embolization syndrome.

This baby was alive.

The, monochorionic co-twin died, a week or two before.

And you can see brain atrophy, a nodular liver of an ischemic liver.

So when one twin in a twin in a monochorionic twin pair dies, the other one is at very serious risk.

Conclusion

So I've come to the end of the, tour of ultrasound of multiple gestations.

We've tried to look at, how we diagnose twins, how we diagnose the placentation type of twins, and how we diagnose twin, twin complications.

And when there are complications, what kind of interventional procedures we can use to try to improve the outcome of one or both twins.

Hope that's been helpful.