“Twin Twin Transfusion Syndrome Part 1: What is TTTS?” – with Dr. Nahla Khalek

Dr. Nahla Khalek is an OB-GYN from the Children’s Hospital of Philadelphia who works in a specialized surgical center for fetal diagnosis and treatment. In this episode, she explains twin-twin transfusion syndrome, a unique diagnosis in which two fetuses share a placenta in such a way that one baby receives “a tremendous amount of blood volume” while the other receives insufficient blood volume. Dr. Khalek reviews diagnostic options, signs to look out for, and more.

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Dr. Fox: Welcome to today’s episode of “Healthful Woman,” a podcast designed to explore topics in women’s health at all stages of life. I’m your host, Dr. Nathan Fox, an OB-GYN and maternal-fetal medicine specialist practicing in New York City. At “Healthful Woman,” I speak with leaders in the field to help you learn more about women’s health, pregnancy, and wellness. All right, Nahla, thanks for joining the podcast all the way from the great state of Pennsylvania. How are you doing?
Dr. Khalek: I’m doing really well. Thank you so much for inviting me. It’s great to talk with you.
Dr. Fox: It is a pleasure, obviously, and we work together professionally on some complicated cases, and based on your position at CHOP, which we’ll talk about, you really get to see some pretty cool stuff, but I think we’re just gonna be talking today about, sort of, bread and butter twin-twin transfusion syndrome, which is quite complex, but we’re gonna really try to, I don’t know, break it down for patients and for women so they just understand what’s going on and what we’re thinking about because this is something that needs to be talked about for women with identical twin pregnancies, monochorionic twins.
Dr. Khalek: Agree 100%. And I hope that, you know, after folks listen to this they’ll walk away with some key points and advocate for themselves as patients, and then maybe sometimes even educate their doctor.
Dr. Fox: So let’s just start with you a little bit, just so our listeners get to know who you are. I obviously know who you are, but tell us, where are you from? How did you get into medicine and OB and what you’re doing currently?
Dr. Khalek: I am originally Egyptian decent. So I’m first generation here, my parents immigrated to the U.S. when I was about 4. And I’m the eldest of three. I’m the only physician in my family. So it’s a really interesting position as my parents get older and my siblings get older, they have a lot of non OB-GYN related questions that I’m supposed to know the answer to.
Dr. Fox: So you’re the chief medical officer in your family?
Dr. Khalek: Yeah, basically for the Khalek household.
Dr. Fox: I know that position well.
Dr. Khalek: But I grew up in New York City, which is always going to be home, even though I’ve been living in Philadelphia now going on 11 years, you know, New York is where my heart is always. And my parents are still living there, and so that kind of ties me to home as well. Grew up in Brooklyn and Manhattan on the Upper West Side, went to Stuyvesant High School for those of the people in New York who know Stuy, and then I ended up enrolling in a combined BS/MD program at the City College of New York, which is now the City University of New York Medical School, transitioned to New York Medical College, did most of my rotations actually on the Upper East side at Metropolitan Hospital, not too far from Sinai. Ultimately, matched to OB-GYN residency in Michigan. So then I spent a good portion of my formative professional years in Michigan and Detroit, where I did my OB-GYN residency and then ended up doing…I’m one of the OGs in terms of combined fellowships in maternal-fetal medicine and clinical genetics. I had to apply to both boards and create a specific curriculum. Now there’s like 14 or 18 combined programs. So just to give you a sense of how old I am. 
And then went back to New York for a couple of years and was recruited to CHOP in January of 2010, which is where I’ve been since. And at CHOP, which is Children’s Hospital Philadelphia, I work within the department of surgery. It is a specialized center for fetal diagnosis and treatment, which basically focuses on families who are affected by a prenatal diagnosis that either encompasses the structural malformation, a genetic disorder, or as the topic of today, a complicated monochorionic pregnancy.
I also love medical education and public health. So during the course of my post-training career, I ended up getting my MPH from Mailman at Columbia and my master’s in medical education at the Graduate School of Education here at the University of Pennsylvania. So I also wear a hat in the med school where I am course director for their humanism and professionalism curriculum during clerkship year. I spend a lot of time on diversity, equity, and inclusion initiatives. I really believe that we need to invest in our young learners, they’re the ones who are gonna end up taking care of us when they get older.
Dr. Fox: Hopefully.
Dr. Khalek: But it also just keeps me on my toes in terms of being, sort of, on the edge and keeping my finger on the pulse of what’s happening in medicine.
Dr. Fox: Wow, that’s a lot.
Dr. Khalek: So that’s me in a nutshell. Also, probably my most proud accomplishment is I have a 2-and-a-half-year-old daughter, Nina, who’s just awesome.
Dr. Fox: Beautiful.
Dr. Khalek: That she’s probably my favorite thing.
Dr. Fox: You are a busy bumblebee. How did you decide, let’s say, once you’re an OB-GYN that you wanted to do A, maternal-fetal medicine, but also the clinical genetics at the same time? Because again, like you said that, that was unusual at the time. It’s still unusual, maybe not as unusual, but what led you to that path?
Dr. Khalek: So when I entered my OB-GYN residency, I actually had aspirations to be a GYN oncologist because I really loved the idea of complex surgery. But also taking ownership of your patients, you know, the GYN oncologists really manage medical as well as surgical concerns for their patients. You know, I know the field has changed, but at the time, they were really the person who was in charge of the patient’s care holistically. And I really liked…I liked the idea of not having to consult everyone for everything and being able to perform complex surgeries outside of just gynecology. What happened was that I did my oncology rotations and did electives. And it was just a lot of death and dying, that was very heavy. I will say that it really, really opened my eyes to the idea of palliative care, hospice care, but also just the strength and grace that people exhibit when they’re under this particular type of duress.
And that’s something that I carry with me to this day. But I felt like I was ineffective. I felt like I’m not making change for these women, even though I admired them and I respected them and I wanted so much for them, no matter how much I had all of that, I couldn’t change things. And then I happened to be in an institution that was a powerhouse for maternal-fetal medicine and particularly prenatal diagnosis and fetal therapy. And I had incredible mentorship. And when I really thought about it, you know, the complexities of performing invasive fetal therapies and, sort of, taking ownership of your patient or analogous to what I was thinking about in terms of GYN oncology, but I felt like I could be more effective and I felt like I could actually mitigate some of the conditions and create a more positive outcome.
So my mind, sort of, transitioned to maternal-fetal medicine. And then within that subspecialty, particularly fetal medicine, even though I really enjoyed the critical care component, I like very complicated things and you can tell, you know, really appreciated the fact that, you know, the maternal-fetal diad was incredibly unique in medicine where, you know, one person was totally dependent upon the other and you can, sort of, get insights into the health of one by looking at the other. And then also with the complex diagnoses, you know, there’s a real role for the idea of palliative care. You know, a medicine can only take us so far and we need to remain humble and always ask ourselves, you know, just because we can do something, is that the right thing? And understanding that there is a certain subset of pregnancies where moms were not gonna be taking their babies home, and how do we support them?
So sort of transitioned into the fetal medicine aspect of things. And I thought that clinical genetics was just a really nice way of marrying and understanding prenatal dysmorphology, particularly when it came to prenatal diagnosis. So it also exposed me to a whole other field of medicine. Clinical geneticists are wicked, wicked smart people, and I thrive in being surrounded by smart people. So that’s kind of how I ended up in, primarily, application of fetal medicine.
Dr. Fox: What brought you to the Children’s Hospital of Philadelphia that we’re gonna call CHOP because everybody on earth calls it CHOP, C-H-O-P? Not because you chop placentas, which we’re gonna talk about, but because of the…you know, it’s just an acronym. So what brought you there?
Dr. Khalek: I was recruited there by my former chief resident, who’s now the medical director and director of obstetrics services here. So she knew that I had an interest in fetal medicine, and she knew I was very, very close to my family, which is why I went back to New York, originally. And she figured out really is not that far from New York. And so I…
Dr. Fox: Figured, why don’t they just pull you away from your family then? Okay.
Dr. Khalek: Yeah. A little bit, not too far. Right. When I came here, I was just so impressed by truly how dedicated folks were towards just thinking about the entire family as a unit and not just looking at mother and fetus as patients, although that really factored into a lot of the decision-making processes, but really exemplified the idea of shared decision-making and also kind of practiced medicine in a way that I always aspired to practice medicine, in the sense that we spent as much time as needed with the families, identified whatever resources they required, and were able to garner those resources to support the family, whether it be a place of safe, food to eat, or a psychosocial, or mental health support, and then really kind of be there at a time where traditionally, you know, everyone, for the most part, can take pregnancy for granted, right, in the sense that about 97%, 98% of the time, everything is cool.
Baby is normal. You have your baby, you go home, it’s wonderful, it’s joyous, but then you have that 2% to 3% of pregnancies that are affected by some sort of structural difference or malformation. And it really does shape your perspective, and it’s very formative in many ways for folks. It was such a privilege, and it was so humbling, and just so professionally gratifying as well as personally defining to be part of that process and experience with families, and CHOP, sort of, had that ideal setting in order to really fulfill that kind of vision.
Dr. Fox: Yeah, I mean, just for our listeners, you know, CHOP is…if it’s not the premier fetal center in the U.S., it’s of the premier fetal centers in the U.S. right. I mean, people may quibble about a handful of places who is, you know, who’s one, who’s two, who’s three, but if you’re not one, you’re one of them, and on the East Coast, that’s where people go for the most complicated fetal or maternal-fetal situations there. And so your experience there is probably different from what most, certainly OB-GYNs, but even maternal-fetal medicine specialists are gonna see and gonna do on a typical day, week, or month. How has it been for you, sort of, you know, being focused on the most complex of cases, as opposed to, sort of, the, you know, run-of-the-mill, maternal-fetal medicine type of things that we deal with all the time?
Dr. Khalek: Very humbling. Like, it’s also, like, professionally very gratifying, right? So it’s a way of collaborating with folks. Like, one of the advantages of being here is that I can collaborate with, you know, radiologists and geneticists and all the pediatric subspecialists, so I can get the benefit of their experience from the neonatal perspective, but then marrying that with the prenatal perspective, you know, it opens their eyes to a lot of different things as well. And everyone here really strives to be at the top of their game. So we all inspire one another and that’s driven by the patients, and, sort of, the complex challenges that they present by virtue of their pregnancies. It’s very, very humbling. It’s very gratifying. It’s very rewarding.
It can also be very, like, heartbreaking. Like, I don’t even know if you can say, like, your heart breaks, sometimes it aches, right, because you can know all the things and do all the things, and the highs are very high, but the lows are also very low. Like, we truly carry every loss with us, and we try to learn as much as possible. And always, always, always with that humility of, you know, is what we’re doing the right thing? It’s very exciting, right? It’s very sexy to think about fetal surgery and operating while you’re pregnant, but you always wanna be mindful, you know, are we really doing the right thing? And, you know, do we think short term, medium term, long term, how do we think on all the terms? And at the end of the day, what we want is for every family to have as healthy of a child as they can possibly have.
Dr. Fox: I wanna focus today’s conversation by saying that I’m right now forewarning you that there’s gonna be more conversations because I’m gonna rope you in as much as possible. But today, we’re gonna talk about twin-twin transfusion syndrome, which we call TTTS just because it’s a mouthful to keep saying twin-twin transfusion syndrome. And this is something that, you know, anyone who’s doing OB-GYN or maternal-fetal medicine and sees twin pregnancies is going to deal with to some degree. But then a lot of those patients, if it starts getting complex, are gonna get sent your way for maybe more evaluation and potentially treatment. So what are we talking about here, with TTTS?
Dr. Khalek: First, it’s a diagnosis that is unique to what we refer to as monochorionic twin pregnancies or monochronic gestations. So that essentially means that you’ve got two fetuses that share a placenta. And you know, in layman’s terms, a lot of people refer to them as identical twins, but we’re appreciating that identical is not always so identical, but within the context of twin-twin transfusion syndrome, essentially, you’ve got two fetuses that are sharing a placenta. And the idea behind twin-twin transfusion syndrome is, even though they’re sharing a placenta, each fetus has their own share or portion of the placenta. And by virtue of being monochorionic, the best way to think about it is you’ve got the umbilical cord that connects the baby to the placenta. And then once the umbilical cord enters that portion of the placenta that’s been assigned to each baby or each fetus, it’s sort of divided into these multiple branches of arteries and veins, think of it as like a tree trunk being umbilical cord, and then all the arteries and veins are all those different branches of the tree.
And it’s those arteries and veins that perfuse or provide a blood supply to what we call cadolidates. So placenta is really kind of like islands of cells and each island has an artery and vein that support it. So the artery is what’s bringing blood from the baby towards the placenta and the vein is what’s taking the blood from the placenta towards the baby. And when we think about arteries and veins, it works kind of opposite in utero because babies are not breathing air. So the fetal circulation is very different from our adult circulation or postnatal circulation in that it’s the vein that’s bringing all the good stuff to the fetus, being oxygen, nutrition, etc. And then it’s the arteries that are taking away all the waste products towards the placenta.
So when you think about the placenta, the placenta is kind of like a heart-lung bypass dialysis machine, and none of us would be here without our placentas. When you’ve got a monophonic placenta, so you’ve got two fetuses. Each one is in their own sac and they each have their own umbilical cord, umbilical cord goes into the share of the placenta that belongs to each fetus. But what’s really unique about these placentas is even though each fetus has its own territory, 100% of the time, you’ll have something called anastomosis, which are actually blood vessel communications. So remember how I said there’s an artery and vein that goes to each cadoline a little island within the placental share. In monochorionic pregnancies, you can have an artery from one baby crossing over and then communicating with the artery of the other baby, or you can have a vein crossing over and communicating with the vein, or you have an artery crossing over and communicating to the vein.
And when you think about the direction of blood flow…So remember how I said the arteries are going from baby towards placenta and the veins are going from placenta towards baby. The direction of blood flow is really driven by pressure. So twin-twin transfusion syndrome is primarily the result of artery to vein communication. What ultimately happens is that you have a redistribution or a change in the direction of blood flow throughout the placenta, depending on the artery to vein communication. There’s no real magic number, but when you have what I’ll put in, sort of, air quotes “enough” artery to vein communications, you then get a redistribution of blood flow where one baby is actually receiving a tremendous amount of blood volume, and the other baby is shunting away from itself, so is not receiving a tremendous amount of blood volume. And it’s basically not an equal distribution of blood flow.
And that results in the phenomenon that we recognized by ultrasound as twin-twin transfusion syndrome. And to break it down even further, it basically means that one baby is hypervolemic, has too much blood volume, and the other baby is hypovolemic, doesn’t have enough blood volume. And so the only thing a baby wants to do in utero is just, sort of, hustle to survive to get to birth. And so what’s really phenomenal is that they start developing these mechanisms to try to adapt to this new distribution of blood volume, and the terms that we use in twin-twin transfusion syndrome, specifically, are donor and recipient. And so the donor is the baby that is moving blood volume away from itself, not voluntarily, but just through these anastomoses. And as a result, decides to be super economic with whatever blood volume it has left. And so what it does, is it shunts or it directs blood flow to the heart and to the brain, everything else gets the leftovers.
And so what you see on ultrasound is less amniotic fluid in the sac for that baby. You see the bladder might not fill and empty, or cycle is the term that we use. And sometimes you might even see a slowing down in the growth of that baby. The only thing that can happen is the recipient baby. So the baby that’s now receiving all this extra volume also has to create mechanisms in order to adapt. And so when we think about the heart, the heart’s a pump and it’s gotta be used effectively to pump all this extra flow that’s going through the baby, and so the heart muscle can get thickened. And sometimes when you think about heart muscle, it’s pretty efficient when you give it a lot of work to do, but when you give it too much work to do, it becomes so thick and it becomes inefficient and those babies are at risk for heart failure. So both babies get sick over time, each in their own way. And it’s all because they’re trying to, sort of, accommodate to this new redistribution, primarily driven by these artery to vein communications that occur within the placenta.
Dr. Fox: If you have someone who has two placentas, right, so a dichorionic twin pregnancy, just so our listeners understand, why would they not be at risk for twin-twin transfusion?
Dr. Khalek: Yeah, that’s a great question. It’s basically because you’ve got two separate individuals living in the same house, right? So a dichorionic twin pregnancy typically is you have two eggs, two sperm, two separate individuals. And so their circulations are never connected. They’re two independent circulations.
Dr. Fox: Right. And there are instances where they’re identical twins that have two placentas, but they would not be at risk for twin-twin, meaning the way we look at it as, you know, obstetricians, maternal-fetal medicine doctors, is the risk of twin-twin is not because they’re identical, it’s because they share one placenta. So if you have identical twins that don’t share a placenta, great, they’re not at risk for twin-twin. They have other issues, but they’re not at risk for twin-twin transfusion, which I think is important because people always ask, are they identical, they’re not identical? Which is interesting for them, but for us, we’re like two placentas or one placenta because that’s the key.
Dr. Khalek: I think also it’s really important, you know, this is where patients can, sort of, advocate for themselves is when you get that ultrasound as early in the pregnancy as possible and they tell you you have twins, you really wanna insist that they figure out if they’re monochorionic or dichorionic, that really helps shape how the rest of the pregnancy goes.
Dr. Fox: Yeah. And if the person doing the ultrasound says, “I can’t tell,” you want a second opinion.
Dr. Khalek: Then you need to go to an…yeah, definitely. If it’s your obstetrician doing it, then you need to say, well, I need to go see maternal-fetal medicine ASAP.
Dr. Fox: Yeah, we had an earlier podcast on, sort of, twinning and the diagnosis and different kinds. And that was one of the things that came up. You know, we know this in our day-to-day work that it’s so critical to know early on, what kind of twins are we’re dealing with here? One placenta, two placentas, all these things because it changes the risk. It changes how we monitor them. It changes how we interpret certain findings. You know, if there’s two placentas and I see different growth in the babies, I know it has nothing to do with twin-twin. It’s not gonna turn into twin-twin, totally not an option. But if there’s one placenta, you know, there’s certain signs that we see that might lead in that direction and it’ll change the prognosis, it’ll change the management. So that’s pretty key. When you have a pregnancy where you know in advance there’s twin pregnancy and there’s one placenta, two questions. What is the likelihood of twin-twin happening to that person? And the second is, is there anything that’s in the control of the patient to increase or decrease, hopefully decrease, obviously, that risk?
Dr. Khalek: Yeah. So in general, if you pull all the literature, the incidence of twin-twin transfusion syndrome in monochronic pregnancies runs anywhere from 10% to 15%, so it’s not insignificant. And as a result of that, you know, one of the, sort of, most proactive things a patient and her physician can do is once the diagnosis is made, you really need to start ultrasound surveillance beginning at 16 weeks. The general recommendation by Society for Maternal-Fetal Medicine and American College of OB-GYN and multiple…Royal College of OB-GYN in Canada, as well as European societies, if you start ultrasound surveillance at 16 weeks then you do it every 2 weeks.
Dr. Fox: Right. And you say that’s when you diagnose a monochorionic twin pregnancy?
Dr. Khalek: Yeah.
Dr. Fox: Right. Now, when you diagnose twin-twin transfusion, meaning before twin-twin, you start the monitoring?
Dr. Khalek: Correct. Yeah. So the ideal is, you know, maybe you get your ultrasound at 8 weeks, 10 weeks, 11 weeks, 12 weeks, make sure to establish chorionicy at that point. And then once you’ve established chronicity, meaning one placenta versus two placentas, if it’s one placenta, you need to start doing ultrasound surveillance beginning at 16 weeks, not coming back at 18 weeks or 20 weeks for an anatomy survey.
Dr. Fox: That’ll change whether you diagnose it, but is there anything they can do to prevent it?
Dr. Khalek: Unfortunately, there’s nothing that can be done to prevent it. Although, the only reason I hesitate is because there is a way to prevent later stage disease and that’s with earlier ultrasound surveillance, but in terms of actually the disease state itself, there’s nothing a mom can do. There’s nothing a physician can do. You’re either gonna develop it or you’re not. And the numbers basically break down to 10% to 15% chance of developing it. You could flip that into an 85%, 90% chance of not developing it.
Dr. Fox: Yeah. And I think, there’s some signs potentially earlier than 16 weeks, you know, that we can see an ultrasound that, you know, might indicate it’s a higher chance of happening is on the nuchal ultrasound we look at and, you know, there’s some signs, but ultimately it’s mostly a matter of, like you said, luck if someone’s going to get it or not get it. And again, on the one hand, it’s sort of a bummer that there’s nothing that either we as doctors or women themselves can do to prevent it from happening. But on the plus side, and what we’re going to talk about, is the early screening, A, you’ll know what’s happening, but B, there’s potential to intervene earlier and then therefore not develop some of the really bad consequences of twin-twin, right? Even if we can’t prevent it from happening, we could potentially prevent the bad outcomes from happening if the diagnosis is made.
Dr. Khalek: Yeah, I agree. I mean, there’s a lot of data that’s being published about, you know, looking at the crown-rump length and seeing if there’s a discordance or, as you said, the nuchal lucency, sort of that fluid behind the neck. Unfortunately, nothing has really panned out that’s a good predictive marker. And so ultrasound remains the mainstay. And at the end of the day, it’s really making that diagnosis of chorionicity as early as possible.
Dr. Fox: Just so our listeners understand, let’s say this was completely ignored, meaning we didn’t think about it, we didn’t screen for it, and it was just left on its own to progress and someone had twin-twin, what would happen to the babies? Like, what are the outcomes we’re worried about if it’s completely undiagnosed and untreated?
Dr. Khalek: Yeah. I mean, it’s really tragic because less than 10% will have what we call intact survival. So unfortunately, one of the, sort of, adaptive effects of TTTS is that the recipient fetus will also develop polyhydramnios. So as that fetus is pumping all that volume, it’s also peeing more, right, it’s making more urine, and that creates an overdistension of the uterus, which can predispose to preterm delivery. And ultimately that is the reason these pregnancies, if they are undiagnosed, can be so catastrophic because they can result in a very premature delivery, with all the consequences of early prematurity. The other consequence is you could have very severe twin-twin transfusion syndrome, which could result in the demise, or the death, of one twin or both twins. And so having it undiagnosed is pretty catastrophic. And fortunately, that is happening less and less.
Dr. Fox: Yeah. I mean, left to its own devices, I mean, you could get “lucky” and have a very mild case and the babies are okay. But the majority of the time, if it’s undiagnosed and untreated, you’re gonna have either two babies that don’t survive or one or two babies that survive and are extremely sick from prematurity or potentially heart failure. I mean, there’s all these problems they can have. So it’s a really big deal.
Dr. Khalek: Yeah. The worst is neurologic devastation. I mean, there are worse things than death, unfortunately. Having two neurologically devastated premature babies is not a good situation.
Dr. Fox: Yeah. So, it is very important. And you said, we start the screening. What is it we’re looking for on ultrasound at 16 weeks, every week or two, when we do these ultrasounds?
Dr. Khalek: If you go by what’s recommended by Society for Maternal Fetal Medicine, we’re measuring the deepest vertical pocket or the largest vertical pocket, or basically the biggest pocket of amniotic fluid in sac and we’re looking for any discordance in that. So the typical general definition is polyhydramnios is when you’ve got more than 8 centimeters that you’re measuring in one sac, and oligohydramnios is when you have less than 2 centimeters. So more fluid or less fluid. The other thing you can identify at that age is whether or not the bladder is cycling, so filling and emptying. And typically over a 20-minute period, you can identify whether or not the bladder is cycling. So a lot of this will also depend on the length of time that the ultrasound examination is being performed. If you’re doing a quick exam, you’re not going to pick it up. But if you spend at least 15, 20 minutes, and you can start at the beginning of the study, looking at the bladder, and then at the end of the study, looking at the bladder and you should be able to see that it cycles.
Dr. Fox: Right. And just to explain what that means, like, you know, in twin-twin ideas, one of them is getting, sort of, overloaded, you know, too much stuff getting pumped in. So they’re gonna be big and plump and peeing all the time. And because of that, their bladder is filled and there’s amniotic fluid all over the place. And the other one is the exact opposite. Like, really, really, like, shriveled up and small and they’re dehydrated, so they’re not peeing. And because of that, the bladder doesn’t fill. It’s like they were, you know, in a desert and they haven’t eaten or drink for, you know, a week. And so you see the discrepancy in the fluids. One has a ton of fluid, one has very little fluid. The nickname we have is polially.
Dr. Khalek: Or it might be a little bit subtle. Like, I’ve got one pocket that’s a little over 8 centimeters, another pocket that’s maybe 3 centimeters, not quite less than 2. So the idea again behind the early ultrasound surveillance is to look for trends more than anything else. It’s very unusual if you’re screening early with ultrasound that you will have, like, a big, big change. Although there have been multiple cases that are referred to us where one week everything looks okay and the next week, boom, there’s a huge difference in fluid. But ideally what you’re looking for is trends. And remember about that donor baby, that donor baby is trying to be super economic. And so one of the costs is that, you know, the blood flow that it does have because it’s preferentially sending it to the heart and brain, the kidneys don’t get as much. And so the kid doesn’t pee as much. It’s not that there’s a missing bladder or anything like that, is just that there isn’t as much volume to distribute.
Dr. Fox: So, how often do you do these ultrasounds on a routine basis? If there’s been no issues, everything’s normal at 16 weeks, you do it every couple of weeks or every week? What do you typically do?
Dr. Khalek: So the general recommendation is if everything looks great at 16 weeks, and there are no subtle red flags, then you can see them again at 18 weeks. And then at 18 weeks, you can also add Doppler studies. So you can look at blood flow patterns in the umbilical artery, and you can also look at blood flow patterns in a very specific artery that’s in the brain called the middle cerebral artery. So all of those, you know, ultrasound markers will kind of help decide, sort of, is this baby or is this pregnancy trending towards a certain direction?
Dr. Fox: Right. And then these are done in all pregnancies where there’s two babies sharing a placenta. Now let’s say there’s a situation where someone might have twin-twin transfusion, or they might be developing it. And this is the point where someone refers them to you. So you have someone coming in, she’s 20 weeks with possible twin-twin, you’re gonna do this. What else might you do in this sort of, like, secondary evaluation where it’s not just a screen anymore, but it’s really, like, for diagnosis and to really map things out? What other advanced things might you be doing?
Dr. Khalek: Yeah, I mean, so we do a detailed anatomic survey. You know, unfortunately, sometimes we’ve had patients referred to us, and part of the reason why there’s a donor and no fluid is because there are no kidneys. So we want to make sure that all the anatomy is there and that’s normal. But one of the other features that we add is specifically fetal echocardiography. And so we look specifically at heart function for both of the babies. And part of that, again, ties into this whole idea of this being a hemodynamic issue, or basically a blood flow issue. And so if you operate under the idea or the premise that twin-twin transfusion syndrome, in many ways, is a result of one baby having too much blood volume and the other baby not having enough blood volume, when you think about what moves that blood volume, it’s the heart. And so looking specifically at heart function also helps inform us as to whether or not this is headed towards twin-twin transfusion syndrome or a different diagnosis, or can inform the severity of the twin-twin transfusion syndrome and how it helps guide management.
Dr. Fox: Yeah. I was gonna ask you because there are different either called scoring or staging systems. I know that you guys have your own CHOP score, you have your own, you know, named score, which is, you know…Congratulations, good for you guys. That’s awesome. But there are many scores out there. I’m just curious. What is the value of having any prognostic score or a stage telling someone yours is a little bit more mild or more moderate or more severe and there’s numbers and different ways to look at it, but just in general strokes, why would that be helpful, potentially?
Dr. Khalek: So it’s helpful, particularly in the early stages of twin-twin transfusion syndrome, to determine whether or not offering a definitive fetal therapy is indicated. So just to give an example, when you have…So twin-twin transfusion syndrome is broken down into stages, right? Stage one, two, three, four, five. As the number increases, the severity of the disease increases. And what’s considered early form twin-twin transfusion syndrome is stage one and stage two. And particularly with stage one, there was previously a tremendous amount of debate as to whether or not we should offer fetal surgery. And the reason being that for most cases of stage one, they tend to stay that way. And so there are risks with fetal surgery, which I’m sure we’ll get into a little bit later on. And so the question is, you know, why take the risk if we know that things aren’t going to change and you’ll still have a generally good outcome?
So that question was answered relatively recently by our colleagues in Europe. And we actually were one of the North American centers that participated. And there were two other centers that participated where we randomized patients who were at stage one to, sort of, determine, okay, if we watch it, versus if we start with therapy, sort of, what happens, and ultimately about 40% will progress. So when we think about the utility of echocardiography, that can sometimes identify the stage one patients who will progress. And when we talk about progression, we’re talking about moving upstage, right, so stage two, three, or four. And so the idea is you’d like to intervene at a point where the babies are not so sick that they would ultimately gain the maximum benefit. So using the echocardiography and understanding, sort of, how the hearts are functioning is very helpful, particularly in the early stages, because then sometimes we can offer surgery before the babies get too sick.
Dr. Fox: Yeah. I think that makes a lot of sense. And, you know, one of the complicating features of diagnosis is, what are we gonna do about it? Meaning it’s not that hard to diagnose twin-twin transfusion, if you know what you’re looking for. Right? Pretty much all of us can do it. But the question about diagnosis is really not just you have it, but A, what is the prognosis? Meaning, what do we think is gonna happen? And that’s highly related to, what are we gonna do about it? Meaning, if treatment is an option, if it’s not an option, and whether we think, it’s gonna work or not work, and those are really intertwined together. So I’m sure when you’re doing the evaluation, part of it is to figure out what’s going on and that the exact same time in your brain is, now that I’ve figured out what’s going on, what are my options to treat and whether they’re going to work or not. And that’s how you counsel people, I imagine.
Dr. Khalek: Exactly. Yeah. That’s exactly how we think about it. So, again, it always goes down to the question about, well, if we do something, is that the right thing to do? And if we do something, what does that ultimately mean for the pregnancy and for the family? So, it’s exactly how we approach it.
Dr. Fox: Excellent. So I think that’s a really good summary of exactly what twin transfusion is, who’s at risk for it, how do we screen for it, how is it diagnosed? And I think what we’re going to do is we’re gonna move on to part two. We’re gonna talk about management and treatment of twin-twin transfusion syndrome.
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