UCSF experts share their approach to evaluating twins in utero, focused on ultrasound detection of those who share a placenta while developing in separate amniotic spaces. Radiologist Vickie A. Feldstein, MD, and perinatologist Nasim Sobhani, MD, provide anatomical keys to anticipating complications, such as twin-to-twin transfusion syndrome. They also present survivorship data from the UCSF Fetal Treatment Center, reflecting the value of early referral for multidisciplinary care.
Refer to Fetal Treatment Center Thank you Aaron for the introduction and thank you all the hosts and the participants for this opportunity. Um Nassim and I really enjoy speaking about this. The notion of twins fills our clinical days. It's a lot the research we do, we do some together and we love the opportunity to learn more and teach more about this. Our title is understanding Monica ionic Miami out of twins they're complications and outcomes. It'll be a split lecture and I will start as Aaron said I'm a member of the radiology department here at UCSF. Our objectives will be to understand placental vascular anatomy, anatomy unique to Monica or ethnicity. I will focus on the ultrasound assessment of monochromatic twins and their complications. And nothing will take over and discuss. Review our our experience at UCSF with non invasive management of some of the complications faced by monitoring the twins. And we have no financial disclosures to report. Mhm. The outline we will as I said, focus on the phenomenon of monochromatic twinning and I will share with you information that sort of came to me in the course of my career at UCSF understanding placental anatomy, particularly the phenomena of placental sharing and vascular anastomosis, how those are manifest both in clinical and sina graphic features and then we'll focus on a few of the complications faced by these twins and review the UCSF management and outcomes. It's really a tribute to the phenomenon of crosstalk between institutions and between disciplines that I was introduced years ago over 20 years ago to Jeffrey Martin who's a now retired fetal placental pathologist who had been based in Oakland and Kaiser. It was introduced to him by cinematographers and he had long been interested in mono chorionic twins, their placentas and their complications. And he shared his whole host of experience with me and all of my colleagues at UCSF. Much of the information I'm going to share with you comes from him and it really starts with a thinking about the phenomenon of monaco chorionic twins. The fact that they share a placenta really best suited to supply nutrition to a single growing fetus. But in the setting of monochromatic twins, two fetuses are aiming to grow in utero and understanding the details of that placental anatomy goes a long way to explain some of the manifestations we see clinically and sina graphically. And I'll tell you I had done this work for about 10 years before I was introduced to Jeff and after I met him and he shared this information with me a lot of cases, not all but a lot of cases made a lot more sense. And it very much informs the work we do day to day. So I'm going to show you some images of placental specimens specimens that he injected with dye to help delineate their anatomy. So this is a monocle chorionic placenta A and B represent the court insertions of the twins. The phenomena will will address when we look at the placental specimens and then some diagram attic um illustrations are twofold. We're going to think about how the placenta is shared. How much of this sort of territory placenta is allocated to each twin. And a unique phenomenon in the setting is the notion of cross talk and virtually all of these monochromatic placentas, there will be connections between the twins, the number, the size and the type of those connections goes a long way to explain how the twins fair in the course of the pregnancy. So in this case, this dotted line indicates where the sort of Equator is where the crosstalk happens and that splits this placenta about 5050. In this example where a has a central court and these court is vela mentis. You can see that the dotted line divides the placenta unevenly More like 60, 40 or 70 30. And you'll also notice that there, it's not near as busy a placenta. There aren't as many vessels on the surface that cross that dotted line. I'm gonna bring your attention to the detailed anatomy. The vascular anatomy along the fetal surface of the placenta and point out um normal anatomy and anatomy unique to monochromatic twins. Normal anatomy and singleton's or twin pregnancies. And their placentas appear as a normal artery and vein pair. And there's a zoomed up view here and it zoomed up, you hear traveling along the surface of the placenta, sort of in parallel and diving down through the uh framing on the fetal surface to bring blood into and then out of placental coddle, Eden. The avian anastomosis, which many of us are taught in training is related to the complications that monochromatic twins face has a unique anatomy where the artery comes from one twin and the vein that arises from that that Katelyn in through that frame and travels not back to the source, but rather across the equator to the co twin. So a diagram attic representation helping explain this phenomenon. In these diagrams, as in fetal circulation. The arteries are blue, so there are two arteries traveling with the umbilical fame to the court insertion, and from that an artery branches out, travels along the surface, dives into the placenta, bringing deoxygenated blood. The returning venus blood is now red, coming back to the source and on the fetal surface from a telescopic view, a normal artery and vein hair. Whether it is in the setting of a singleton pregnancy or a mono chorionic twin pregnancy would look something like this. This is another close up view of a not very complicated placenta if you will, with a solitary artery to vein anastomosis injected placental specimen, and this is what it looks like. Close up. You can see one vessel coming from the left and the companion vessel traveling to the right. There was a long held misconception that the artery to vein anastomosis that occurs in the setting of monochromatic twins were hidden deep within placental perama. Couldn't be seen. Couldn't be addressed. Couldn't be treated, but in none of the placentas that I showed you. Or we'll show you, will you see a solitary vessel diving down without a companion? So the misconception of avian anastomosis long held was this fact is the avian anastomosis that occur in monochromatic twins either from A. To B. Or B to A. Have a more predictable anatomy. And as I said, the two branches of that connection died through the same hole. And look roughly like this from the endoscopic uh view. And simply that understanding of what the anatomy of an avian anastomosis is I think helps me understand better. Help me frankly find them with ultrasound. No, we don't have to spend our days doing that. They are actually findable. And they're quite I'm comin there's another connection I want to bring to your attention. Whether it is worth paying attention to. I would submit. And that is this yellow vessel running right along the surface of this monochromatic placenta without diving down without changing color. This phenomenon unique to monochromatic twinning is an artery to artery anastomosis. So dye was injected into the umbilical artery of one twin, it crosses through this connection and fills to the base of the co twins cord. Uh The drawing is a little bit unnecessary but for completeness sake, I'll show you this artery to artery anastomosis. The cut surface and then the fetus topic view. It's blue because it's an artery without receiving oxygenation through the placenta. Coursing from one chord to the other. I'm now going to share with you some of the diagrams that dr Jeff nation of created in the course of his eight year career um studying mono chorionic placentas in a single center here in Oakland. And what I want you to be aware of is the sort of variety in what we might see and how that links to the post natal outcome which is recorded here as well. So here's an example of a twin a marginal to the left and twin be marginal to the right. There's quite a lot of connections back and forth between their circulations, red and blue and blue and red. So these are bi directional artery to vein and Eskimo seas and in the middle there's a continuous blue vessel artery to artery. It is therefore not that surprising that this twin pair fared fairly well and we're only 6% discordant. They have connections that allow their circulations to equip vibrate and a fairly even split of the placental pie in this case. Again, the placenta is fairly evenly split with much fewer connections. But those connections are balanced. HIV in one direction, a tv in the other direction and also note an A to a anastomosis. This twin pair was only 3% discordant at um delivery. And one last example um. Uh This is a twin pair that was complicated by twin twin transfusion with the recipient twin central court insertion and the donor twin a The momentous court insertion. Few connections and unbalanced with net flow from donor to recipient and 32% discordance. One last example sorry. With bidirectional connections but unequal sharing you can see that the equator would be in this location between a assuming the majority of the placenta be a much smaller share. But um with with adequate bidirectional connections and an artery to artery anastomosis. While they were discordant, there was not the complication of twin twin transfusion. I share all that with you to help you understand what I came to understand by reviewing this information with dR mitch in that. Thinking about the placenta as the source of much of what we see when we manage these pregnancies. Thinking about how those, how the placenta is shared and how many connections and the type of them helped prepare us for what we may see as the fetuses grow. The first publication from this rich data source was a series of looking at the placental, announced and moses and this one selected cohort and the risk of twin twin transfusion. And it's a busy full slide of our abstract presentation but will bring your attention to the phenomenon of what kinds of connections were seen and the associated risks. Yeah. Through in twin transfusion was much more common in those cases who had a placental review artery to vein anastomosis only or artery to vein with a rare vein to vein anastomosis. In other words, those in whom an artery to artery anastomosis was present faced much lower risk of twin twin transfusion. The summary of that data shown here we the series included all twin pregnancies delivered at Kaiser northern California in this six year period. They are all the placenta is referred to a single site and underwent detailed exam by a single examiner by dr Minchin. It included a series of 639 and as I said, we looked at the number and pattern of those connections. The incidence of twin twin transfusion in that series was not as high as you might read in other sources, only 8%. It's pretty safe to say that all monochromatic placentas, virtually all monochromatic placentas will have connections. And the most common combination is an artery to vein. As I showed you and an artery artery. As I showed you, those who did not have an artery to artery were much more likely to develop twin twin transfusion. You can see the numbers here. The rate of twin twin transfusion with an A. V. Only was 49% with an avian BV was 78% and the number is much much lower when an 80. When an artery to artery was present artery to artery anastomosis allow sort of a pop off valve for blood to return from one twin circulation to the other. And so that that piece of information for me, understanding that there was an entity such as an artery to artery. And this message which has not had not been something I knew of or heard of and recognizing that it's common but not always present when present. It allows twins to re equip vibrate, thus protecting them from the complication that we've been taught to look for and worry about To take away. In the 639% is reviewed in the series. Those with a anastomosis had a 5% rate of twin twin transfusion. It doesn't eliminate the risk but significantly reduce it and those without a anastomosis faced a 47% rate. And we're focusing on our experience at UCSF informed by data that came from Kaiser. But I'll tell you we are not the only researchers to make this observation and added to the literature. So that's how the vascular connections inform how the twins fair and specifically their risk of twin twin transfusion. I also referenced that placental sharing can be variable. Um so from a similar series this time. 644 placentas. We looked at birth weight to scored. Its thinking about this phenomenon of if the placenta is shared on evenly. How does that influence how each twin groves. We like others use the definition of birth weight discordance greater than 20% is considered discordant. And the Assessment of unequal placental sharing is a visual one. Looking at the injected of placental specimens drawing that equator and determining that unequal sharing was when the ratio was 60, 40 or more unbalanced. Okay mm hmm, cord insertion sites. As I showed you in those diagrams and placental patents. Path specimens. Um correlate with how placentas are shared. The combination has shown here of a central and peripheral. Either Marshall or Velma Mantis Cord is a proxy for a placenta that's not very evenly shared. The odds ratio in this series was 5.4 and then unequal placenta sharing As manifest by how the where the equator lies. Is a predictor for discordance and birth rates. More unequal sharing, sort of no surprise associated with more discordance and birth rates with an odds ratio of 9.83. All of that helps me understand when I do an ultrasound in the second trimester, monochromatic twin pair. The likelihood that the twins will run into trouble or if I'm seeing early complications. Understanding the underlying ideology for what we're seeing. The notion of unequal placental sharing goes a long way to explain a lot of the cases that we are sent to evaluate. Um Keep in mind it doesn't it's not the same phenomenon as twin twin transfusion but dia grammatically what you'll see is a central cord in a typically normal grown twin with normal fluid and a marginal Orvella mentis cord and a smaller twin with possibly decreased food but not necessarily all of the hydra videos and that can be correlated with birth weights such as this discordance in size. So the more I thought about the placenta's I've seen directly path specimens, the placenta's I've imaged with ultrasound. The more I would submit. Yeah, the variety of monaco chorionic twin placentas is like snowflakes. They're all the same phenomenon. But they have unique characteristics, particularly regarding how their shared and the vascular connections. And those underlying differences. Help predict and explain what we see when we do our ultrasound and ultimately clinical assessment. So, I'm going to go through now the ultrasound assessment of monochromatic twins, particularly complicated monochromatic twins. And at this point when a acknowledge one of the medical illustrators with whom we've used in creating the visual information chris um Gray lap is a really helpful contributor. The ultrasound assessment. As in all your practices of course would um include confirming mono chorionic die amniotic uh twin pregnancy. We assess carefully the placenta that's shared and the inter twin membrane. Every study would include a reporter the deepest vertical pocket of amniotic fluid. For each twin, remembering that to qualify as a vertical pocket, it must be at least a centimeter wide. Also, we'll report when we do by aama tree will report the percent discordance and estimated weights and the formula here is the larger weight. The weight of the larger twin minus the weight of the smaller twin divided by the weight of the larger twin. I don't know if it's routinely done in all practices. It didn't used to be ours, but I would submit in this setting. It's really helpful to address the court insertion, easier done earlier in pregnancy. The court insertion for each and in our setting there is sometimes spent usually a pretty straightforward assessment looking for an artery to artery anastomosis. I'll show you how that's done given that it pertains important difference in the risk between my face. The assessment of court insertion and detection of an artery to artery anastomosis is way more straightforward and an anterior placenta. So that's the example I've shown here, a central cord for one twin, a marginal record for the other. And with color. Doppler settings sort of uh medium lee a set from medium sensitivity. What we're looking for is a vessel running between the court insertion sites, usually pretty direct path. When sampled. Very characteristic wave form and sound. It's a vessel connecting to beating heart. So it's a bidirectional pulse, a tile arterial flow. And what you might see on color is something like this with red and blue and red and blue and back and forth. So that's an artery to artery anastomosis. That um we can help in our counseling of a family, let them know that that means that there's a much lower risk of developing twin twin transfusion. And frankly the majority of monochromatic twins without complications. Well grown, normal fluid harbor and artery artery anastomosis. So if time allows you might well try your hand. It finds you. I do want to talk briefly before nassim takes over about some of the non invasive management of complications. We see a few words about the entity that we're all concerned about. When we assess these twins, specifically twin twin transfusion syndrome. We saved that specific diagnosis for when we see can accommodate all of the hydra. Meows and polly hydrangeas in a model chorionic. Yeah. And the fluid is discrepancy or one is abnormal. We don't use the term twin twin transfusion and sort of strict about assigning TTS label for concomitant all ago. And polly um with the donor manifesting Olivo and the recipient. Polly keep in mind they may or may not have discordant estimated weights that's not necessary for the diagnosis. The staging I'll return to in just a moment. True twin twin transfusion. When you use the definition in this strict way carries high risk of mortality and morbidity for both donor and recipient and in utero intervention is offered in our setting and others, which can improve outcomes, particularly for stages 23 and four. So I've listed the Quintero staging scheme here as a reminder. Stage one is can comment all ago and polly Pocket less than two and pocket greater than eight for donor and recipient respectively. For stage one of the urinary bladder, for the donor must still be visible In stage two. There's all going polly but no longer visible bladder in the donor abnormal doctors in either twin would be labeled stage three high drops in either stage four and demise of one or both. The stage five. So stage 23 or four are candidates for intervention. And an example here diagram attic and phonographic was a case I remember well who came to us at 23 weeks, six days. And this is the manifestation of stage four. Twin twin transfusion. The donor was stuck with no visible bladder. The recipient had polly and as you'll see in this image manifestations of high drops. So clearly they were um highly likely to have a very bad outcome if there were no intervention offered. So the intervention when we do it is to a blade. Those connections in general, the twins who run into trouble and necessitate an intervention. Have few connections. Generally unbalanced connections with an artery arising from the donor circulation supplying a coddle Eden from which a vein drains to the recipient. I've never seen a placenta is simple and straightforward as this but in theory it could happen because there's such a range of snow fights. But in general what we're looking for in these settings is unbalanced a tv connections with net flow of blood from donor to recipient. And no anastomosis allowing for return. So you saw the diagram attic representation of an avian anastomosis. We know what we're looking for. And our goal, telescopic lee is to insert a device that obliterates the flow in those two limbs of the avian anastomosis. It's a tiny structure. We're chasing a huge room full of people. Um This is an example of twin twin transfusion requiring intervention. This being stage two with no visible donor bladder, luckily there's some more straightforward procedure with the poster placenta. But wherever the placenta is, if the procedure is necessary, we find a way to insert a scope into the polyp hydra, amniotic sac of the recipient and I'll show you now what this looks like when we when it becomes necessary, what we do. So the scope is now looking at the court insertion of the recipient, twin a central cord. Not much cross top. Not much action, but a pivotal positive artery to vein anastomosis for looking catastrophically straight down at that connection. We're coming to it Now with the laser, the membrane is off to the right, the donors step off to your right, The artery is darker than the vein. So we laser bleeding flow in the arterial then first then taking the major language in acting it and now obliterated flow in the venous limb of this positive baby anastomosis. That's the intervention when it's necessary. Um So I will come back to any questions regarding the faster connections and sharing phenomenon and the role we play when we do our best and assessment. But now I get to introduce my colleague passing savant who will talk about complications in our experience and create. Thanks Vicky. So I'm going to speak specifically about our single center experience with expectant management of three unique complications of mono chorionic diameter pairs as just a caveat. This is not an exhaustive review of the literature or a summary of the various practice patterns or outcomes across the country or even the global experience with these conditions. But instead we want to really highlight our centers experience with non invasive expectant management for these conditions where there is still a considerable amount of debate as to whether intervention would be beneficial. And so to start I will start with just defining the three conditions that we're going to discuss. And then you'll see for each of them. I'll go through what our experience has been in terms of natural history and the potential predictors of progression of advanced stages of that particular condition. So the first is Quintero stage 1 2 and twin transfusion syndrome. So I'll go hydrangeas in the donor and Paula hydrangeas in the recipient. Um Like dr Feldstein just reviewed the next is what we are calling part or poly hydrangeas affecting a recipient like twin where the normal twin has a normal D. V. P. So not all go hydrangeas and not polly hydrangeas. But then the other twin which we label as recipient like does have pollen hydrangeas. And we're seeing increasing number of these cases referred to our center. And so we um we're interested in sort of seeing what their natural history was, what their rate of progression to true twin twin transfusion was. Um So this is sort of a new entity that we are focusing more on now and then the last is unequal placental sharing. Where there is this discordance between the fetal weight in the twins, there's not necessarily a discordance in their fluid and they don't have features of 21 transfusion syndrome or of part and the difference in the percentile, the difference in the estimated fetal weight is at least 20 percent or more. I think we'd also like to make sure that this is sort of distinct from selective fetal growth restriction. So the E. F. W. For both of the twins is above the 10th percentile. So the smaller one is not meeting criteria for birth restriction. And I think the other thing to note is that this is really a combination of a normally grown twin and then a relatively under grown twin rather than a normally grown twin and then a larger twin, so it's really normal and then relatively smaller. The other definition I'll just go through is sort of this naff net overall outcome which is a nice way to combine just sensational Asia delivery as well as survivorship for mono chorionic periods because both of those things are really important. So a good outcome is considered dual live delivery at 30 weeks or beyond. Of course with no demise. A fair outcome is either a dual live delivery sometime between 26 and 30 weeks or a single demise And then a poor outcome is a dual live delivery less than 26 weeks or dual demise. And so we'll go through again each of these conditions and talk about progression but also overall outcome in the good fair or poor sets. So starting with stage one E. T. T. S. This is our experience with all of the monaco chorionic diameter twin pairs that refer to our center in a 10 year period. Um and had stage one T. T. T. S. So looking at the sort of natural history, we saw that 72% of these remained stable, so did not progress to a higher order T. T. T. S. For improved and um in which the tts actually resolved In looking at survivorship, 90% had at least one surviving twin and 72% had dual survivorship. And then looking at those overall outcomes, we saw a two thirds of them had a good outcome of dual live delivery app or beyond 30 weeks and then 17% with a fair outcome in 17% with a pour out. So overall watching really closely and waiting and not necessarily inter meeting appeared to have pretty good outcome for these modi twin pairs with isolated stage one twin twin transfusion. We were next interested in looking at the gestational age at delivery in this group as a whole and the median gestational age was 31. Um nearly 31.5 weeks. Then we wanted to determine whether there are any predictors. So looking at the group that stayed stable or improved and comparing it to the group that progress to a higher order T. T. T. S. And thus would have been eligible for an intervention. So um some of these p values you'll see don't quite reach the standard statistical significance of 5% but they are quite close. So looking at the week gestational age at initial diagnosis of stage one, you can see that those who progress were generally diagnosed at an earlier age and that makes sense theoretically as to why they would be more likely to progress. Those who had a small bladder in the donor or only a bladder that was intimately visible. They also had a higher rate of progression on the order of 50% compared to 14%. And I think this is a really important thing to remember because oftentimes when we're doing these ultrasounds, we think of the concept of the bladder being present, or a fluid filled bladder being present or absent as if it's di economists. But if you're doing these ultrasounds like dr Feldstein and many of our colleagues here, do you will notice that there are some cases where the donor bladder just looks smaller throughout the whole exam or you start the exam and initially you don't see a fluid filled bladder In that donor and you keep going and then 45 minutes later finally you get an image of a flute felt better. So that's the image that you take. That that case is probably not the same as a case where you see the fluid filled bladder throughout the entire exam. And so I think that's sort of an important nuance to remember when we're thinking about interpreting these ultrasound results and it appeared to be a potential predictor of progression in these stage one cases. And then we are examining for a and estimates is and all of these twins and we thought that maybe there would be a difference between those who were stable and progressed. This was not significant or close to significance in terms of our statistical analysis but just looking at the numbers that sort of looks like maybe it might be productive if this was replicated in a larger company. So putting that all together in terms of our approach at UCSF. Generally we prefer expectant management for stage one T T T. S because like I said, the majority of them remain stable or improved and two thirds of them have the overall good outcome of dual live delivery at or beyond 30 weeks. And we know that in utero intervention carries procedural risks. And so when we have an alternative option to intervention, which is this expectant management, it's we have to weigh sort of as risk versus benefits. We would say that of course close follow up is recommended. So 27% of these progress and so more frequent ultrasound imaging and clinical visits is certainly warranted for these cases. And I will say that this is a similar conclusion was reached from a recent Nafta RCT of laser versus expectant management for stage one twin twin. That included a primary outcome of survival without without significant neurodevelopmental issues at six months. And they found no difference in the two groups. And so it's really sort of been um corroborated in this bigger sort of multi center study that expectant management really is the way to go for these Stage one cases. So the next condition I'm going to review is part or poly hydrangeas affecting a recipient twin. Um Again, this hasn't been described as much in the literature but it's a fairly common indication for referral to our center. So we've had a number of these patients over the past many years. And so this is our experience of all the mono chorionic diana twin pairs that were referred to us over about a seven year period and were diagnosed with just parts just poly hydrangeas. In one of the twins. Um 77% of these were stable or improved, so did not progress to TTT. S. And in terms of survivorship, 91% had at least one survivor and 86% had dual survivorship And then looking again at those NAFTA overall outcomes. We found that 80% had a good outcome of dual live delivery at or beyond 30 weeks. 15% had a fair outcome in only 5% had a poor outcome. And the average gestational age at delivery was just shy of 34 weeks. Which is fairly on par with most mono chorionic twin pregnancies. In looking at predictors of which cases progressed to T. T. T. S. Versus which remain stable or improved. We did see that there was those that had a higher discordance between the twin with polly hydrangeas, the recipient like twin and the normal twin they were more likely to progress. And those that had a greater discordance at diagnosis were actually less likely to progress. So they were more likely to remain stable or improve. And then looking again for that A a and estimates this again, we see that sort of protective effect of this very specific inter twin connection where those who had a a president were more likely to remain stable rather than progressing onwards to T. T. T. S. So again our approach is to expectantly manage these cases since many of them remain stable or improve and since the vast majority of them do have a good outcome rather than offering intervention um as a sort of stage zero T. T. T. S. Or stage 0.5 because of the procedural risks that we know come I'm with in utero intervention as I said before with the last condition of course close follow up is recommended. I think it's important to know that 23% of these in our series ultimately developed T. T. T. S. And that is a higher rate than the general mono chorionic diameter twin population where we think that they're you know on average there's a 10 to 15% risk. And so those who present with polly hydrangeas and one of the twins they seem to have a higher risk and so warrant closer follow up rather than just saying oh well they don't have T. T. T. S. So they can continue their sort of routine. And then the last condition I'm going to review is this unequal potential sharing. So again this concept of a relative discordance in the size of the twins without frank growth restriction of the smaller twin. So this was all of our twin pairs referred to our center in an 11 year period who had an inter twin E. F. W. discordance of at least 20%. Um And not including those. Again who had a diagnosis of frank growth restriction at the time of their industry presentation In looking at their outcomes. We found that less than 50% remain stable or improve. So actually the majority of them will go on to develop selective fetal birth restriction and I'll talk about that in just a little bit Survivorship overall was very high. So 97% with at least one survivor and the same percent with dual survivorship. And then looking at those overall outcomes combining the survivorship and just special Agent delivery. We found that 73% had a good outcome of a duel live delivery at or beyond 30 weeks. 23% had a fair outcome and only 4% had a poor outcome with an average gestational age at delivery being 33 weeks. Which against pretty good for a complicated mono chorionic twin brother see in terms of predictors of who progresses ultimately to the development of selective fetal growth restriction, surprisingly the week's um uh just facial age at the time of initial diagnosis of unequivocal center sharing did not appear to be different between the two groups which was an interesting finding and not necessarily what we were expecting. Um The degree of discord and set diagnosis appeared to be a little bit different. It didn't quite reach statistical significance but maybe something to explore there and then um the presence of an a an estimate this in this case did not appear to make a difference in terms of those who progressed to selected fetal growth restriction and those who remain stable. And that's not entirely surprising because we really talk about the presence of an a a being protective against the development of T. T. T. S. And that path of physiology is very distinct from the passive path of physiology of unequivocal central sharing and selected fetal growth restriction. So our general approach here is to um wash full meeting expectant management of these growth distorted twin pairs that don't have selective growth restriction. Again because they tend to have a fairly good outcome in terms of 73% having this duel live delivery or beyond 30 weeks. And because we know that in literate intervention like they've said so many times carries procedural risk but it's not just the procedural risks of the potential um interventions that are issues but actually thinking about anatomically what the procedures do and how they actually may predispose to greater risks specifically in the setting of unequal placental sharing. So there are some centers that have advocated for the same sort of laser procedure that's done for twin twin transfusion. To apply that to unequal placental sharing the idea that you're sort of going to die korean eyes, the placenta sort of split them by um laser in a way that intertwine connections. But the truth of it is in these in these twin pairs where they have unequal placental sharing, It may be that those connections are actually very important for that smaller twin and that that smaller twin is sort of recruited more of those connections just supported itself. This concept of sort of a rescue transfusion. So it's been given a sort of smaller piece of the placenta pie. So then if you laser through those connections now you've left that smaller twin with a much smaller portion of the placenta. And without those rescue connections which may actually further increase the risk of developing growth restriction or maybe even precipitate an interview and fueled the lives. There are other centers that will discuss selective reduction for these cases where there is unequal placental sharing but not quite fetal growth restriction yet. And the idea that a selective reduction is a sort of controlled um uh controls demise as opposed to the risk of a spontaneous demise in a monochromatic pair which would carry a significant amount of risk to the surviving. Yeah, But in the various series that have been reported specifically on using selective production for this indication there's a fairly high risk of co twin loss on the order as high as 50% in some studies which is really high. And when we look at art, when we Examine our series of these cases, the risk of a spontaneous um interview during fetal demise was only 4%, so so much lower than what I think is sometimes out there. And what might be driving the counseling behind selective production. So again, close follow up as usual is recommended because this is unlike the other two conditions, the majority of these cases do ultimately progress. So more than 50 of 50% of them will develop selective growth restriction and the mean gestational Asia which they developed that it was about 27 weeks. There's sort of two interesting points about that. One is that the new investigational agent diagnosis of selective fetal growth restriction in our cohort was 27 weeks. Um but overall in the entire Cohort, that mean gestational agent delivery was 33 weeks. And there is actually no difference in between the two groups. So those who did develop growth restriction and those who did not, there wasn't a difference in their gestational agent delivery. And then in thinking about why 27 weeks might be the time in which this fetal growth restriction manifest. There's a lot of interest in sort of the plasticity of the placenta and the way that a mono chorionic placenta can grow over the course of pregnancy. And other studies that have really looked into the sort of placental functioning have demonstrated that 26, 27, 28 weeks, that's around the time where the monochromatic placenta sort of reaches its peak of growth and then plateaus after that point. So it may be that up until that point, the monochromatic placenta is continuing to grow and so it's able to supply the smaller twin, but then it sort of reaches this tipping point where it's no longer able to continue that supply. And that's when we see this manifestation of the machine, I will summarize what I've covered and add a few tidbits that coincide with what nassim shared. So thinking about monochromatic twin pregnancies, I will recommend that I would submit actually that it will work for you. Like it has for me to think about the placenta that each twin pair shares. Think of it as a snowflake unique to that twin twin pair. You're evaluating and understand this whole phenomenon as a rising in large part. Not entirely, it doesn't explain all the challenging cases we see but it goes a long way to explain uh the outcomes. If we think about the placenta they share how it's shared. I recommend careful assessment of court insertions mostly with attention to marginal of elementaries which we lump together in our analyses as peripheral. So a central cord and the peripheral court is a set up for an unequally shared placenta which then may correlate with discordance in the estimated weight. You see we do that calculation. Big weight on a small weight divided by big weight. And those who are over 20% sort of get our targeted attention and lots of follow up and parenthetically I'll say If you take two twins, one's normal size spot on 50th%ile and do the math. And imagine a co twin that was 20% discordant at 33 weeks. That discordant smaller twin Dropth below 10%ile and would qualify as selective growth restriction. So it all sort of goes together that way vascular connections you saw what a normal a. V. Pair looks like. Yeah these are called avian osteoporosis. It's actually not the best term because it's a normal artery and a normal vein. Um But what's abnormal is the artery comes from one twin and the vein brings blood to the other. So anastomosis. When we think of avian esteem, Asus and other body parts and other parts of medicine. It's a pathologic vessels, normal vessels with an unusual unique situation and then recognize that there is this um um unique kind of connection and artery to artery anastomosis which can have characteristic wave forms. And um spectral doctor sounds. And our data as as well as others have shown the protective effects. Why some of the twins we see don't run into trouble. Um So the assessment I would reinforce these two recognize monaco dynasty as early as possible in the years we've been doing this when very positive trend has been how much earlier women recognized their carrying monochromatic twins. And much earlier detection of complications. Much earlier referrals which helps us optimally managed and intervening when necessary. The deepest pocket is part of that assessment for each twin. The calculation as I said, of their um discordance in their estimated weights, we report the court insertions and look as I said, for the artery, the artery anastomosis. And then this is just a summary of those three conditions. So looking at the risk of progression um the likelihood of a good outcome again that dual live delivery of both twins that are beyond 30 weeks. The average gestational agent delivery and the potential ultrasound findings that are that could be predictors of the likelihood of progression and that's all we've got. We're happy to answer questions. Thanks everyone for your time and attention.