Multigestation Imaging: Diagnosis and treatment options

Recently, we have been seeing multiple gestation pregnancies at increased frequency. This is most likely due to assisted reproductive techniques. But imaging of these multiple gestations can be challenging. So here, Dr. Beth Klein-Fath from Cincinnati Children's Hospital Medical Center, Department of Radiology, is explaining multiple gestation imaging. Multiple gestations uh represent about one to two percent of all births and have really increased since the 1980s because assisted reproductive techniques. So there are two types of multiple gestation, dizygotic and monozygotic. So we can either have uh fertilization uh of two eggs. Which makes dizygotic or fraternal twins. On the other hand, monozygotic twins are actually splitting of a single ovum and result in identical twins and it is a constant epidemiology for monozygotic twins. So what does determine chorionicity? Obviously, if they're different sex, uh that's very helpful because then we know they are dichorionic, but looking for two separate placentas um is very helpful and that can be difficult especially later in gestation. So using transvaginal ultrasound, we can start to see the appearance of the membrane as early as five weeks. And we can actually start to see what kind of membrane we're dealing with at less than 14 weeks. So in dichorionic uh membranes, we have lambda appearance and that's because we have chorion between the two amniotic membranes. Whereas in monochorionic twins, we have two amniotic membranes with no interposed uh chorion. So we have this T-shaped pattern. What about mortality rate? Do they change with the types of multiple gestation? As you can see with the different types of twin pregnancies, as we get into the monochorionic gestations, we have a higher mortality. We know that monochorionic pathologies represent 73% of twin intrauterine deaths. What are the main causes of this? Congenital malformations and definitely placental insufficiency, but the big ones are due to vascular anastomosis. And vascular anastomosis is a condition when blood from one twin, the donor, is pumped through an artery or vein into the shared placenta. And then drained through an artery or vein into the circulation of the other twin, the recipient. And the one which is imaged the most is twin-to-twin transfusion syndrome or TTTS. But we do also see twin anemia polycythemia, single twin demise, and twin reversed arterial profusion syndrome. Um just remember that in monochorionic twins, we have a higher risk for cerebral findings. Let's talk about TTTS first. It's seen in about 10 to 20% of monochorionic diamniotic gestations, untreated, has a very high death rate and we also know uh is associated with brain injury. Tell us what are the variations? And we can have uh many different types of anastomosis, one being artery to artery, the other being vein, vein to vein. And then we have the dreaded arterial venous anastomosis. And when that occurs, we obviously get too much blood going to one twin, which is causes heart failure, and then the other twin suffers from placental insufficiency. So how does this affect fetuses? What are the differences between donor and recipient twins? So in the donor twin that uh actually is suffering from placental insufficiency, we develop hypovolemia, oligouria, oligohydramnios, and growth restriction as we can see the difference between size of these two twins. And then the recipient is hypervolemic, polyuric, uh has polyhydramnios and cardiac dysfunction due to volume overload. I got it. So then what are we supposed to see on the Doppler imaging of the recipient twin? The recipient twin is the one that has too much blood flow and is the one that's going to have heart failure and those twins tend to have venous Doppler abnormalities. Um we can get a pulsatile umbilical vein. What about the donor twin? The one with the placental insufficiency. What do we expect to see on Doppler? Those uh fetuses often have no bladder and you will typically see arterial waveform abnormalities. So there's something else we look at on Doppler imaging, right? We also look at the middle cerebral artery because we can tell when there's been redistribution of flow to the brain um because of a dysfunction. And as we know, this dysfunction is not necessarily TTTS. We can also see it in congenital heart disease and intrauterine growth retardation. Also, multiple gestation imaging is not limited with ultrasound or Doppler. We also can use fetal MRI. There's ischemia in the brain, which is often identified by germinal matrix hemorrhages. So, we have used fetal MRI uh to look for brain injury in these twins before and after therapy. We can see certain patterns in twin twin between the donor and the recipient and we found fetal MRI to be helpful prior to laser intervention and in the counseling of these families. So what do we do for TTTS? Is there a treatment? Well we do selective fetoscopic laser photocoagulation in these twins, so we're going to laser the vascular anastomosis. And this procedure has changed the survival rate of twins, which is a game changer. And now we have survival in 80 to uh 90% of these twin gestations. Let's talk about twin anemia polycythemia syndrome or taps. Twin anemia is a inter-twin hemoglobin difference, and we don't really see the signs of twin twin and that's because it's very small AV connections across the placenta. So why don't we get oligohydramnios and polyhydramnios like we see in TTTS? Is there any relationship between TTTS and taps? We can see it spontaneously, we can also see it after laser in twin twin transfusion and sometimes see it in the second and third trimester. Here's the most important question. How do we diagnose it? We actually use the middle cerebral artery Doppler. We are now um moving to a new staging system where we're using just the differences between the middle cerebral artery between the two twins. As we do get into the later stages, we're either going to do transfusion or laser to help these uh twin gestations. So here's this important point. There are other signs to help us diagnose taps. We may see a starry sky in the liver of the recipient, and then sometimes we'll see differences in echogenicity between the placentas. So what happens as far as brain injury after laser? Let me explain it with a study by Sternman and all. They looked at this and saw after laser surgery, 2% of the cases had brain injury, and mainly those cases had recurrent TTTS or taps. Now let's talk about single twin demise or what used to be called twin embolization syndrome. So what happens when one twin dies? We used to thought it was an embolic event, but actually it is shifting of blood. So we have blood that actually reverses from the live fetus to the dead fetus. Ah, that happens. So the live fetus becomes hypotensive or develops hypoperfusion and can experience tissue necrosis in the brain and kidneys, right? And there was a nice study that showed that one in the surviving had um brain injury um and that correlated with advanced gestational age, twin twin before demise, or lower gestational age at birth. Finally, twin reversed arterial perfusion or trap. We know that this is the most extreme version of TTTS. We see it in 1% of monochorionic gestations, and this is an artery to artery anastomosis between the two twins. When we talk about trap, we designate the receiver as the acardiac twin, and the donor as the pump twin. The cardiac twin has unoxygenated blood, then we have abnormal development of the twin. These twins have 100% mortality. 100% mortality. Wow. I guess that's why we consider these cases extreme. On the other hand, the pump twin has been cited to have a higher risk for chromosomal abnormalities, but more importantly, they can develop congestive heart failure and have polyhydramnios and hydrop. So how do we diagnose it? Well, basically we're going to look for differences in arterial flow. What about the prognosis? How do we decide? We can look for cardiac disease in the pump, we can look at the volume of the cardiac, cord entanglement, which can also be a source of problems in these twins. And what do they look like on ultrasound imaging? A cardiac twin can look like anything from solid tissue to dysmorphic tissue with swelling to a fully formed twin that mimics the appearance of discordant twin. Here is the pump twin when very sick, you can see the heart gets very big and the twin is very hydropic. Last question, is there any intervention to treat this extreme condition? What can we do for these twins? We're going to do cord ligation for these a cardiac twins when we're concerned that the pump twin may have demise. Now I got it. So essentially, monochorionic twins are more of a concern mainly because of the vascular anastomosis, regardless of it being artery to vein or artery to artery. They all have high risk for CNS injury and malformations and for that reason we um often do fetal MRI to look at the uh brain.