Sonography of Twins - HD

Introduction

Hi, I am Debbie Levine.

I'm a professor of radiology at Harvard Medical School and I do ultrasound at Beth Israel Deaconess Medical Center in Boston.

Today I am going to be giving a talk on ultrasound of twins.

Risks of Twins Compared to Singletons

As I'm sure you're aware of, it is more dangerous to have twins than singletons, both for the mother and for the gestations themselves.

Perinatal mortality increases as the number of babies increases.

So twins and triplets are going to have a higher perinatal mortality rate.

And this is old data, but it still holds true today.

And part of that is because twins, triplets, quadruplets, higher order multiples are delivered earlier than do singletons.

And you can see that in this chart.

Again, old data, but still very true today.

But there's another reason why twins have increased morbidity and mortality, and that has to do with the fact that they can also have congenital malformations.

So if you look at the risk of twins, and here when I say die, die on this slide, I mean die amniotic, die chorionic twins.

So this is the safest type of twins to have.

They are of course at risk for preterm delivery.

And because of that, we look at the cervix and we start checking the cervix in the second trimester.

They're also at risk for growth restriction because they need a little bit more from the uterus than does a singleton pregnancy.

But they're also at increased risk for congenital malformations.

And you can just think of this as when twins happen, when the egg splits, the later the egg splits, the more likelihood there is to be an abnormality.

So diamniotic di chorionic twins can be identical twins depending on when the egg split and when implantation occurs.

And that's the main reason why they have increased congenital malformations.

Types of Twins Based on Egg Splitting

When you look at diamniotic monochorionic twins or the DMO twins, they're also at risk for everything that the dye dye twins can have.

But they can also have twin twin transfusion syndrome, which we'll talk about in detail later.

An even later split will be the mono amniotic monochorionic twins, the Momo twins.

They'll have all of the problems that the other type of twins can have, but they can also have cord entanglement.

And I've got an image on this slide of a twin.

And you can see many of the problems that twins can have.

This is the left side of the chest.

The heart is clearly on the right side of the chest.

There's Dexter cardia.

You can see that there's lung disease here from the prematurity.

So there's respiratory distress syndrome, and you can even look at the bowel with all the small bowel over on the right hand side.

There's malrotation of the gut as well.

So here's another old study looking at twin morbidity.

A survey of almost 34,000 women. 1.3% had twins.

Preterm delivery affected 54% of the twins and only nine pro 6% of the singletons.

And the twins, even though it was only 1.3% of the deliveries, they accounted for 15.4% of the neonatal deaths and 9.5% of the fetal deaths.

So let's now go into when the egg splits and how that affects the type of twins.

And this is an image from human embryology and it shows that about one third of all twins come from one egg and two thirds of twins comes from when the woman ovulates twice.

And there are two eggs. So these are the fraternal twins, these are the identical twins.

If you then take these one third of all twins that start out from a single egg, depending on when they split, depending on when they implant, you could end up with two separate placenta or you could end up with one choon.

Um, and two amnon, again, two separate placenta or the, or the Momo, um, twins.

So the monozygotic twins monozygotic, they come from one zygote, they come from one egg.

Um, if they split on about day three or before, um, you end up with the die die twins.

That's about one third. If they split on day four to seven, that's the DMO twins, which is about two thirds.

And if they split after the first week between day seven and 12, you end up with the Momo twins.

And then much later splits are gonna be the very rare conjoined twins that we see in about one in 50 to one in a hundred thousand births.

So just to recap, dizygotic coming from two fertilized eggs, two thirds of twins.

And this is affected by maternal age, race, and parody.

The monozygotic twins are one third of twins.

About one in 250 are not so much affected by those other risk factors.

But anyone that deals with a population where they have a lot of the infertile couples that are being treated by many different fertility factors know that will end up with a lot more of these dizygotic twins.

But we also end up with a lot of monozygotic twins as well.

Importance of Chorionicity and Amnionicity

So multiple gestations ity is important and it's important because of those abnormalities that I discussed earlier.

And it's also important because when one twin dies, it makes a difference whether they're sharing a placenta or not.

So we look in the first trimester and if we can clearly see that there are two separate gestational sacs and a thick dividing membrane, maybe we'll even see two separate placenta that's very clear that that's going to be a die die twin.

Now here we've got one placenta and it's really difficult to see this membrane.

You really have to try hard.

This is the classic thin membrane that you'll get with diamniotic monochorionic twins.

And you need to spend time looking for this very, very thin membrane.

It gets harder and harder to see later in gestation.

And this is important because mono amniotic twins, when there's no amnion in between these two twins, they are purposely delivered very early to avoid that complication of cord entanglement and demise.

First Trimester Ultrasound Scanning

So why do we do endo vaginal scanning in the first trimester?

It is so that we don't miss twins. Here's a nice example.

We're looking transabdominally through a full bladder.

There's a retroflexed uterus and there's a gestational sac back here, and we're not seeing much within the gestational sac.

You do a vaginal scan, you'll get your probe much closer to this gestational sac, and you can actually see that there's two yolk sacks here.

Now you might wonder, how do I know these are dimo twins?

Where is that very, very thin amnion between these two gestational sacs?

Well, I know it's monochorionic.

There's one big gestational sack here, but we're not seeing the amnion yet because it hasn't completely formed.

If you think about what you see early on in gestation, you see the yolk sac first, then you see the embryo, and then you start seeing the amnion after about seven weeks.

So it's just too early to see the two amnon.

So if you have two yolk sacs, you know that two AMNs will eventually form.

And that's how I know that these are dimo twins.

Now, classically in the literature it's described as a thick membrane is greater than two millimeters, and the thin membrane is this little wisp of a membrane here, less than one millimeter.

But sometimes it's difficult.

You just see something, you're not sure if it's thin or not.

What else can you do? Well, here we can actually see that there's two separate amnon.

That's how thin that little amnion is.

We're just seeing a specular reflector there.

Sometimes you can see two separate placental sites and that's how we'll know that they're dye chorionic twins.

And later on in gestation, if you look at the guidelines for scanning twins, one of the things to do is to look at the gender of the twins and to actually put that in your imaging report because obviously if there's one boy and one girl, unless something very bizarre has happened after the egg has split, uh, these are going to be di chorionic diamniotic twins.

So the dimo twins should be the same gender.

There should be a single placenta and there should be this very thin membrane between the twins.

Discordant Twins and Chorionicity

So getting back to Coic city, we look at Coic city because we wanna know how to think about discordant twins.

Now of course, you can have discordant twins if one of the placenta is very small, if the cord is inserted in the membranes instead of the middle of the twins.

And if there's anomaly in one twin, but not in the other twin.

Um, but discordant twins in size makes up this, think of twin twin transfusion.

And twin twin transfusion can only occur if there's a single placenta.

As I said before, the later the egg splits, the more likelihood there is to be congenital abnormalities.

And that's why the DMO twins have a higher incidence of congenital abnormalities than do the die die twins.

But fetal death of one twin is exceptionally important because if one twin dies early on, it's a die die twin.

It really doesn't add any increased risk to the pregnancy.

But if the die mo, if a second twin dies after the point in time where the little connections in the placenta have developed, then the surviving twin is at risk for other anomalies and also for demise.

Now, we don't do as much amniocentesis now as we used to in the past, but if you're going to do an amniocentesis, it makes sense that if the twins share placenta, they share chromosomes.

And so you might not need to do an amniocentesis in each of the different sacs if you're looking for, uh, what the karyotype actually is.

But if they're dye dye twins, you can't know if they came from one zygote or two.

And that's why if you do an amniocentesis of dye dye twins, you actually have to do an amniocentesis separately of each sac.

So dye dye twins have this thick dividing membrane.

They may or may not be of different genders, they should have separate placentas.

Although sometimes you can imagine if both placenta implant anteriorly or posteriorly, sometimes it's difficult to tell.

Um, you look for a thin membrane and you look for the so-called twin peak sign.

We can see a little bit of it here and let's go into that in the next slide.

So the idea behind the twin peak is that if you have a dye chorionic placenta, some of that placenta tissue actually can grow in between the two leaves of this membrane.

Whereas if you have a monochorionic placenta, you just have the two Amnon here and you shouldn't have placental tissue in this little triangle.

And here we can see nice placental tissue in this twin peak.

And again, you can see how thin an amnion is.

These are the two choon. And here's the other amnion.

So here's an example of diamniotic monochorionic twins, Dimo twins.

You see the one Corian, you see the two Amnon got a little bit of the embryonic poles here and a little bit of a yolk sack here.

Twin Mimics and Special Considerations

What about twins that look like this?

Well, again, we're going to spend a lot of time looking for that dividing membrane to see if we can see it.

And, and you can see on a later, little bit later in gestation, here's that very, very thin amnion, definitely worth the time taken to look for it.

Now a twin mimic is a signia.

If you look at this image here, you might think you've got two separate gestational sacks, but all you have to do is turn your probe and see that this does not go all the way across.

So this is a signia. It is a scar within the uterus.

Please don't call this an amniotic band or an amniotic sheet.

People will confuse that with true amniotic bands.

This is just a signia, it's a scar within the uterus.

It should go side to side, but you should usually be able to get another image that shows that the amniotic fluid cavity just drapes around it.

Here's another twin, mimic a bicornuate uterus where you have a desigual reaction in one side and the gestational sac in the other.

And if it's ever unclear whether you're just dealing with a bleed on one side or not, you can just bring the patient back in a few days and hematomas will rapidly change.

Sometimes you'll see a funny appearance when you're looking at the membrane and you see a little bit of fluid between the two membranes so you can see that they're separated.

Uh, this can sometimes happen after an amniocentesis is performed.

If you go through the two different membranes, you can get a little bit of a leak here.

A lot of different case reports, case studies and descriptions have been written of this.

But basically it doesn't matter if you see it, you really don't need to worry.

IVF and Heterotopic Pregnancies

Now, I mentioned the IVF population before and the fact that twins and multiple gestations are exceptionally common in this gestation.

And we need to be very careful when we see an intra in gestation in somebody who's undergone in vitro fertilization that we look for a second gestation that might be inside or outside of the uterus.

So if you take a person who just walks in off the street with a classic rule addict, ectopic pain, pregnant, first trimester bleeding, and you look at that person walking in off the street, they have like a one to 2% of an ectopic pregnancy if you don't see an intrauterine pregnancy.

But if you take someone in the IVF population, they walk in off the street and you see an intrauterine pregnancy, they also are at one to 2% risk of having a coexistent heterotopic pregnancy.

So in this IVF population, always look for the second gestation, always look for the twin, look for it both inside and outside of the uterus.

And I say here on this slide, regardless of the history, make sure when you see twins that they're actually in the uterus.

So this is somebody with no history of in vitro fertilization, came in with, uh, who was pregnant, having pain, and we see an empty uterus here, we look out in the annexa and there are two separate gestational sacs, two separate gestational sacs, each one with an embryo.

Although this one was much larger than the other, this actually looked more like a fetus at about 13 weeks gestational age.

This was about eight weeks.

And uh, this is what it looked like afterwards, that there were two different gestational sacks outside of the uterus, twin heterotopic pregnancy.

And when you see two gestational sacks, don't forget to look for the third.

Um, and of course that's gonna be more common in the in vitro fertilization population, but you always wanna count clearly, make sure that you're not missing a third gestation.

And here we can see d chorionic, tri amniotic triplets.

So that we've got two big gestational sacs, we've got three dividing membranes between them.

It's harder to see the dividing membrane here.

So you're gonna have two choon, three amnon diatribe triplets.

Counting Twins and Vanishing Twin Syndrome

Well, I mentioned counting of twins.

And it's important if you're counting twins early to realize that there might not be as many later because of course, one, uh, cannot survive.

But you might also miss some early.

Um, so if you look at twins, and again, this is a rather old paper from 1998, but uh, from my own experience, it's rather similar now.

So they looked at twins greater than six weeks, who were studied early, early on five to 5.9 weeks.

And they found that 11% of the die die twins were missed.

86% of the dimo twins were missed.

And so think about it, the die die twins is where you're gonna see the two separate gestational sacks.

The dimo twins is where there's only the one big sack that you'll see early on, and that's why you're gonna miss more of these dimo twins.

But again, sometimes they'll be twins initially and one will not survive.

And then you can have this vanishing twin phenomenon.

And it turns out that about 21% of twins verified to be alive, meaning you see a heartbeat with sonography disappear.

Subsequently, um, if it's in the late first trimester, even early second trimester, typically there's no risk to the living co twin.

So here we're looking at, um, twin gestational sacs.

One's larger than the other. Um, so this is at seven weeks.

Uh, one we saw if embryonic pole with a heartbeat.

One had a smaller yolk sac, no heartbeat.

And when you look at it later, 10 weeks, so three weeks later you see, um, a live, uh, fetus in one side and just a residual sack in the second side.

Now sometimes when a patient comes in with an appearance like this and they haven't had any prior scanning, rather than invoke a dead twin, um, I will say that I see a little bleed on the other side because if it's not going to be a viable pregnancy, um, and if you're not sure if it's a bleed or a second gestational sac, why get the patient concerned, um, about that second gestational sac.

Um, I used to say this all of the time, and now we have a little bit more of a problem with this, with all of the tests that are being done, um, with the cell-free DNA so that they're taking the maternal blood and testing it.

And you can imagine if this was an anomalous twin that didn't survive and this was a normal twin that did survive, and when they're looking at the maternal blood, they're actually looking at cells from the placenta, you might get some contamination.

So there is a reason in somebody who's going to be undergoing that cell-free DNA to mention these, uh, second gestational sex.

So you need to be a little bit careful in wanting to protect the parents from thinking about the loss of a twin and knowing if the patient's going to do that cell-free DNA study later on in gestation, if a demise has occurred later in pregnancy here, for example, we can see a bit of a fetal head at about 20 weeks, and here we can see a residual crown rump length, um, in a smaller gestational sac, uh, that's beginning to resorb so that the gestational sac itself is smaller, the embryo is smaller, obviously there's no cardiac activity.

This will become smaller and smaller and smaller over time.

Now sometimes you'll see twins of different sizes and they'll each have a heartbeat.

And these we're gonna follow very, very carefully to make sure that they both stay alive and most likely, um, the one that's lagging behind will end up dying.

It is of course possible for a woman to get pregnant and the next month to ovulate again and get pregnant again and have twins that are four weeks apart.

But that's very, very unusual.

And in a case like this where you see one twin measuring about seven weeks, the other twin measuring about six weeks, um, that's not going to be the case.

A woman won't ovulate seven days apart.

So the fetus papus is when there's a small non-viable fetus in a small sac.

And over time in gestation you'll get flattening necrosis and atrophy.

And when they look at the placenta, um, at pathology, they'll actually be able to identify this.

Twin Anomalies

So let's now move on, uh, to the twin anomalies.

And there are two main reasons, uh, for the anomalies to occur.

One is this embryologic hypothesis.

Monozygotic twinning is a result of abnormal embryonic development and therefore is associated with other anomalies.

So here, um, are some mono amniotic twins.

We're not seeing the membrane between them very well, but it was, I'm sorry, this is a d diamniotic monochorionic twin.

We're not seeing the amnion very well, but we are seeing that there's anencephaly, there's no ossified skull above the orbits in this twin.

This twin looks normal.

Of course, we can also see growth discordance in twins and growth discordance greater than 20%.

Um, of the estimated fetal weight will be worrisome.

Here we're looking at twins, and in one of the twins, all the biometry parameters are 24 to 25 weeks.

The other twin, they're more like 20 to 22 weeks.

And the abdomen circumference is really the smallest at 20 weeks.

This is classic growth discordance with IUGR in the smaller twin.

Impact of Twin Demise

Well, what happens when one twin, um, dies if they're monochorionic, if they're sharing a placenta, if you look at six weeks and see two heartbeats, it turns out that about 40% will end up with two live born and 30% will end up with one live born.

If you see two heartbeats at 12 weeks, 75% will end up with two live born and 0.5% will end up with one live born.

So something's happening between six weeks and 12 weeks when the twins share a Corian.

And this is what's going on behind the anomalies that you see in association with twin, twin transfusion syndrome.

You can end up with one live born early on because when one dies, it doesn't necessarily lead to the demise of the second twin.

But later on, once they have these vascular connections, if one dies, the other one uh, will likely die as well.

Twin-Twin Transfusion Syndrome (TTTS)

So this is what we see when there's twin twin transfusion and you end, end up with a stuck twin.

This twin is stuck because there's no amniotic fluid around it.

The amnion is holding onto this twin very, very tightly.

This twin is floating around because there's all this polyhydramnios.

So twin twin transfusion occurs in four to 35% of monochorionic multiple gestations.

The perinatal mortality is very, very high and it accounts for a large percentage of twin mortality, and it's all because of these vascular anastomosis.

So these are some rather gross, literally gross pictures of twin twin transfusion where you have the donor twin who ends up being anemic, having growth restriction and oligohydramnios, and the recipient twin who ends up with polyhydramnios polycythemia and hydrops.

We define the features of twin, twin transfusion in part, but not completely by growth discordance.

So fluid is important, and size is important as well.

Estimated fetal weight difference 20%.

And the abdominal circumference difference of 20 millimeters, um, the sensitivities are 80 to 90% positive predictive value, 70 to 80%.

So obviously growth discordance isn't good enough to be sure that something is twin, twin transfusion.

Um, so we're gonna look at the placenta as well and actually look at the vessels that connect these two twins.

And what happens is that you end up with both superficial and deep connections that can be connections between the arteries, between the veins or an artery to a vein.

And these artery to a vein connections are the one that lead to unequal sharing.

And you can imagine it's because one twin is having arterial blood going and it's going from a, a high resistance to a low resistance system.

And that's why you'll end up with the unequal sharing of blood.

So here's a rather old study looking at placental anastomosis in in twins with without twin twin transfusion.

And it turns out, and this is a little bit counterintuitive, that the PLN from twins with twin twin transfusion actually had fewer anastomosis than controls.

And the way you can think about that is that the more anastomosis you have, the higher likelihood is that the twins can actually end up more equally sharing the blood.

And so they can make up for some of these unequal sharing conditions.

Um, and there was no significant correlation between the number of anastomosis and the inter cord distance.

So here is, um, a nice placenta study where they've injected different colors into the different twins, um, umbilical cords, and you can see how the vessels spread out from where the umbilical cord insertion site into the placenta is.

And here you can see one of these connecting vessels.

It's also interesting if you look at this plate between the circulations of these two placenta, you can see that there's some other connections, for example, up here.

And you can also see how one twin has more of the placenta than the other twin.

And that's why, um, sometimes you'll just see growth restriction even if there's not twin, twin transfusion.

When we look at the vessels that connect these two, we actually look at the wave form to figure out if these are artery to artery or artery to vein connections.

There's an artery to artery connection in this example.

And here's an artery to vein connection, um, in this example looking at the flow here.

So, um, this is a nice diagram showing what happens that you've got these connections, this is what we're seeing on the surface of the placenta, but the connections are actually a little bit lower and deeper within the placenta itself.

Treatment of TTTS

So there used to be a lot of therapies for twin twin transfusion.

Uh, the first of these was amnio reduction.

Um, if you've got an anomalous twin, sometimes people will very rarely do the selective feticide, but you need to make sure that that doesn't lead to the twin embolization syndrome.

So you have to be very, very careful if you're ever gonna do that.

But what's more commonplace done now is the laser ablation of placental anastomosis.

And these have reduced fatalities from twin twin transfusion by more than 50% at this point.

Now, I also wanna make you aware of this TAPS syndrome, which is a twin anemia polycythemia syndrome.

And this is in that spectrum of twin, twin transfusion, but doesn't quite get there.

You have one twin that has anemia, the other twin that has polycythemia.

Some people do a lot of doppler studies to look at this, and there are different charts that you can look up to see if the peak systolic velocity differs between these twins postnatally.

When you look at these taps, uh, uh, neonates, uh, they end up with hemoglobin differences at birth.

But for twin, twin transfusion, the real twin twin transfusion, there's this so-called quintero staging that most people use.

Now, if you get down to stage five, it's death of one of the twins.

It's too late to do anything.

If you're at stage one, you might just see that there's a fluid difference with the maximal vertical pocket, the MVP less than two centimeters in the donor sac and greater than eight centimeters in the recipient sac.

In these cases, you wanna look at the bladder because if the twins are processing fluid normally through their kidneys and excreting them normally into the bladder, and then, uh, urinating and making amniotic fluid, you should be able to see the bladder in each of the twins.

Stage two, you'll see absence of the urine filled bladder when you've got this discordance in the amniotic fluid.

Stage three is when you get the doppler abnormality.

So you might have absent or reverse end diastolic flow in the umbilical artery, reverse flow in the ductus osis or pulsatile umbilical venous flow.

Um, and then stage four is ascites, pericardial and pleural effusion and hydrops.

So we know we can't intervene at stage four and a lot of people just watch at stage one.

And the real question is, uh, when you intervene at these stage two, three, and four, does it improve outcome enough to make it worthwhile to do when you have a case of twin twin transfusion?

So here's a study looking at the stage three and four twins looking at laser versus amnio reduction.

And they ended up with similar numbers of survivors, but they ended up or two survivors.

So they both lived, but they ended up with a higher number where there was at least one survivor.

Um, and, uh, miscarriages, double fetal loss, uh, neonatal death.

And an interesting one, abnormal brain scan.

This is very interesting because it turns out that when one twin dies, and I'll get into this in a little bit, and the other one survives, you can end up of course with the twin embolization syndrome, but twin, twin transfusion itself can lead to brain abnormalities because of the unequal sharing of blood.

And the theory is that they're hypoxic incidents that happen.

So when you do the amnio reduction, you end up with a higher number of these un abnormal brain scans.

If you look at the birth weights of the donors and the recipients, they're both better in the laser group.

And, and this was one of the early studies, but it really did show, uh, that it for at least for stage three and four, it's worthwhile, uh, to do the laser ablation.

So looking at imaging fluid discordance, this is an extreme case again, and you can imagine if this woman was turned on her side that this stuck twin back here would stay stuck and this twin would float.

So sometimes, um, if the stuck twin is posteriorly located, you do have to move the mom around to get that image of the stuck twin.

But regardless, you should always look on both sides of a membrane, even if the membrane's very difficult to see, to see how much fluid there is.

You also get the feeling from this image that this twin is smaller than this twin.

Brain Abnormalities in Twins

So this is one of the dreaded white matter abnormalities that we'll see in twins after one demise.

And this is what leads to cerebral palsy.

This is encephalomalacia that we're seeing here.

And you can imagine this area of white matter in the brain is also gonna end up with a cystic encephalomalacia later.

Now, sometimes we'll be, uh, scanning a fetus, there'll be residual one fetus that is still alive when we'll be asked to do magnetic resonance imaging to look better at the brain.

Um, this is that same twin done on exams just within two days of each other.

And you can see all this brightness lining the ventricle here is actually what was left of the cerebral cortex, and that most of it had just melted away because of this diffuse encephalopathic process that happens, um, after there's death of one twin.

So this is what we look for.

And the question is how can Mr be helpful?

Mr can be helpful because you can see the abnormalities probably about a week earlier before you see them with ultrasound.

And it's also going to be sensitive for some of the smaller and, um, earlier abnormalities.

So again, going back to twin anomalies, the thromboembolic, uh, theory is that there would actually be little emboli that come after one twin dies, and the ischemic theory has to do with the shared placenta.

And when one dies, it kind of acts as a very low resistance resistance system, and all of the blood from the live twin kind of goes out and rushes out.

And so you end up with ischemic infarcts within the live twin regardless of the etiology.

Microcephaly, multicystic, encephalomalacia, which I just showed you, hydrocephaly hydrocephaly, limb amputations, intestinal atresia, and skin abnormalities are all things that we can see.

Acardiac Twin

So, so far I've spoken about the die die twins that are mostly at increased risk for growth problems in early delivery.

The d mo twins, they share a placenta and they can also be at risk for, uh, the, the twin twin transfusion syndrome.

And now we're getting into one of the really rare abnormalities, the a cardiac twin.

So by definition, these are monochorionic.

There has to be a vascular connection between these twins.

And if you think about it, one of the twins just doesn't have a normal heart.

So a cardiac is a little bit of a misnomer.

It might be that there's no heart or no functioning heart, or it might just be a very, very poorly functioning heart.

This happens in about 1% of monochorionic twins.

You end up with an arterial connection from the good twin from the pump twin with an arterial anastomosis, uh, to the recipient twin.

And so you have puls atal flow from this good pump twin going into the internal iliac arteries of the twin with the poorly functioning heart.

So structured supplied by the distal abdominal aorta and the iliac arteries are developed best, and the upper trunk and head are not adequately perfused.

So if you look at an a cardiac twin, you'll see something like this, a little bit of a blob with legs, and then here you've got an image of the donor twin.

So you've got the retrograde blood going in this direction.

If you do a pulse stopper, you'll see the flow going into a twin, the arterial pulse flow going into the twin, the venous flow going out.

And the problem is that this twin is doing all the work for the other twin and for itself.

And so you can end up with cardiac and failure and death in the normal twin.

And so we watch these very, very carefully and we don't intervene until this a cardiac twin gets large enough to cause a pump problem.

Uh, for the donor twin, this is what an a cardiac twin will look like on a gross specimen.

You can see there's not much of a head, maybe a little bit of an arm here, but that the lower limbs are actually developed because the arterial flow again, is going into the iliac arteries.

So here's an example, um, from my own institution just kind of watching what happens with twin, twin transfusion Early on, um, we had an 11 week gestation, and this is twin A and here was twin B.

There wasn't a heartbeat. There's some edema here.

So this was just thought that it would go on to be, um, a demise.

But um, as we followed this, here's the little membrane between the two twins that twin bee started to get bigger and shows this classic configuration of twin, um, a cardiac twin where you get all of this soft tissue edema.

So I have some images, um, of the edema in this, a cardiac twin.

And you can see how if there's all this edema that the pump twin's probably doing a lot of work to help sustain this.

And so there are a number of different therapies that we can do, uh, for these a cardiac twins.

And once they get large enough that we actually want to intervene, when they can interfere in the growth and normal development of the recipient twin, that's when we'll actually do something.

So here we're looking at the recipient at the donor twins.

Um, and you can see age by dates 20 weeks here, the age by ultrasound, um, 18 weeks, six days, uh, femur length, abdominal circumference, slightly smaller, um, than the head measurements.

And when you look at the cardiac twin, you can see that the puls to flow is going into that twin.

And there's frequently just a very, very small distance between the umbilical cord insertion site and where it's going into the abdomen of this twin.

Now, I thought it was interesting in this case that they asked for an MRI.

I don't think an MRI was really going to be needed, but, um, the reason for doing the magnetic resonance imaging study was to look at the donor twin, make sure that there weren't any brain abnormalities before we went and ahead and did one of these procedures that can be done to actually ablate, um, the donor twin, I'm sorry, the recipient twin.

So here we are in the ultrasound room, um, with the different people going in and here we're doing an actual laser ablation and going just right into the cord insertion side of this twin and heating it up and ablating that twin.

Now you might, uh, go back to everything I said about twin embolization syndrome and wonder how safe is it to do this procedure?

And the idea is that since the donor twin is actually giving all the blood to this twin, there's not going to be one of those periods of hypoperfusion when there's like that watershed when one dies.

So all of the blood flow belongs to the donor twin in this case, and, and therefore it's not as dangerous.

You can see all the artifact here that's caused from, um, this procedure that we're doing.

Uh, the procedure though is not without risk.

Uh, here you can see that the, uh, twin that we ablated gets smaller over time, but there was some cho amniotic separation.

And that makes sense. Anytime you intervene, um, in a pregnancy, you can actually cause cho amniotic separation and other, uh, problems with preterm delivery.

Amniocentesis in Twins

Well, what about doing amniocentesis?

If we're gonna talk about doing procedures in twins, and I mentioned if they're monozygotic, if they share the same chromosomes, it makes sense that you wouldn't have to do an amnio of each of the twins.

Every now and then though, you'll have what are clearly monozygotic twins and they'll have different anomalies.

Uh, so you can have a different phenotype even though the genotype is the same.

Usually they'll have the same karyotype, but every now and then they'll have this very rare post zygotic non-disjunction where they just haven't split evenly.

But in a case like this, this was a case of of triplets, but when there, there was a monochorionic pair, one of the triplets clearly had big cystic omas and, and was having all of the skin thickening.

It had a small stomach and was felt to likely have Turner syndrome, the other one looked totally normal male.

Um, and you can have mosaic, uh, turner syndrome where it's, uh, the, the karyotype, um, doesn't necessarily affect the abnormalities that we see.

And when these twins were born, they actually each had, uh, Turner syndrome.

Monoamniotic Twins and Conjoined Twins

All right, let's move on now to twins that have split much, much later.

And these are the Momo twins, mono amniotic mono twins.

We only see one yolk sac in these twins.

Again, we need to follow it up, uh, because with early dimo twins, with early mom o twins, it might be that only one yolk sack is seen.

You can actually miss the second yolk sack.

So the mom o twins, um, can have conjoined twins if they split exceptionally late cord entanglement leads to perinatal mortality and 30 to 70%, and that's why they're watched so carefully and delivered at around 34 weeks.

They, uh, get their heart tracings monitored once they've reached the age of viability.

And, and like I said, they're delivered early.

So when you look at twins like this and you don't see a membrane between them, and maybe the heads are together, you actually wanna spend some time and see if they'll move separately.

And if they move independently, um, that lets you know that they're not conjoined twins.

Cord Entanglement in Monoamniotic Twins

Cord entanglement. How do you diagnose that?

Well, you see the cord, it looks like a mess.

Um, and you can put your pulse doppler on it.

I'll show you that in a minute and actually see two different wave forms.

So here, um, there, this was a study looking at cord entanglement in non coin conjoined mono amniotic twins and cord entanglement was present in, uh, four of them and was missed in one.

And you can imagine cord entanglement, that's how you get the knots.

That is what can lead to in utero demise.

So here we're looking at a cord and I've got my, my spectral doppler gate, my pulse doppler gate between two different vessels here within what looks like maybe one cord, or maybe it's a tangled cord, and we've got an artery and a vein going in different directions.

And, and that's what you would expect, um, to see.

But if you get two different arteries going in two different directions and the heart rate is actually different, that helps you know that you've got, um, the knot or the tangle within the cord that you've got that cord entanglement, not, not necessarily a knot.

And here both of the arteries are going in the same direction, but we've got slightly different heart rates that you can see, um, as they go in and outta phase with each other.

So sometimes you can actually see the cord make an X like this.

Uh, here's one very, very early on with cord entanglement.

And this is what they can look like at delivery where they're totally tangled up within each other.

Conjoined Twins

So conjoin twin one in 50,000 to one in a hundred thousand births, these are always going to share a placenta.

By definition, they're not gonna have an amnion between them.

These are mo mo twins.

This is what happens when the egg splits in the second to third week, um, after it's been fertilized.

The site and extent of fusion varies and congenital and abnormalities are always present where the fusion is.

But they can also be present separate from the region of union.

And again, this just goes along with that rule.

The later the egg splits, the more anomalies are there.

So these conjoined twins have different names coming from, um, Latin and depending on where they're conjoined.

So the pagus is where they're fastened.

Cranial pagus is when they're fastened at the head.

Thoracopagus is when they're, um, fastened at the thorax.

Um, fallo pagus at the abdomen and the thoraco and fallo pagus where they're, uh, conjoined at the thorax end, the abdomen is the most common.

So here we've got heads that are conjoined.

You can see some cystic hydroma here.

Here we've got abdomens that are conjoined.

You can see ascites around it.

And here we've got legs that are free floating, but they're facing each other.

And if you were to keep on scanning this, you would never see these legs change in their orientation.

Well, that was an old study.

Here's a little bit of a newer study showing you how much better ultrasound has gotten in the past 20 years.

And here we can see the thorax with a heart that's being shared.

You can imagine how incredibly important that is at the time of diagnosis, because when they, when we're looking at these conjoined twins and the surgeons are talking to the parents about how they might be able to split them after birth, who has what, which twin has what, who has the anatomy, who has a heart that can sustain a twin, that becomes very important.

Here we're looking at the abdomen, um, with livers that are shared.

Here's a small bowel that's shared lower down in the pelvis where they each have a bladder.

One of these twins of a conjoined pair had a two vessel cord.

One of these twins had scoliosis, obviously away from the area of where they were connected.

And one of the twins had a unilateral cleft lip, again, away from the area of where they're connected.

So once you see conjoin twins, you wanna do a really good job looking for other abnormalities.

Here's another example of conjoined twins.

These ones, um, that were just together low down.

Although the heads look close here, they actually changed in position with respect to each other.

And you could actually look at the vasculature that was connecting these two down low.

Here's a, a fetal mr looking at conjoin twins.

And I have to say that our surgeons really do like the mr looking for associated abnormalities.

And again, for surgical planning, I feel very comfortable looking at an ultrasound and saying what's combined.

Uh, but the pediatric surgeons and the parents definitely have an easier time understanding the MR images.

Here's another Mr. Case of twins that were sharing ahead at 30 weeks.

Um, looking at other abnormalities, there was a single kidney, single bladder sustaining these two.

Um, and these are the heads after the babies were born.

Conclusion

So this has been a whirlwind tour in about 40 minutes of twins.

We've talked about how twins develop, um, that congenital anomalies are are common.

Um, that we always wanna look for growth because discordant twins are very common.

Choicy is important. We're gonna look for it in the first trimester when or the earliest point in time when the twins are noted, because the anomalies that they get are going to depend on how late the egg split.

If they have a single placenta, we're gonna think about twin, twin transfusion, and we're gonna be very careful if there's death of one twin.

Um, dimo twins are of course, at increased risk for anomalies and demise after there's death of one twin.

And again, it might mean that you only need to do one amnio instead of two.

Um, the amni is also important, and that's because the mono amniotic twins are at such high risk, not just for anomalies because they split late, um, but also for the cord entanglement, conjoin, twins, um, that and the fact that there can be demise in utero, uh, because of the cord entanglement.

So I hope that, um, you found this talk interesting and that the next time you see a singleton, you'll look to see if there's a twin.

Thank you.