Fetal Intervention 101: Monochorionic Twins, Twin-Twin Transfusion Syndrome & Spina Bifida

[Dr. Anthony Shanks]
Can you tell us what conditions does a fetal interventionalist treat that maybe a maternal-fetal medicine wouldn't?

[Dr. Hiba Mustafa]
I also want to mention why do some people call it fetal therapists? Usually, when you hear the name, you think it's surgery. It's not necessarily surgery. It's really any intervention that you think might improve our outcome. It could be simply medical therapy. It's either surgical or medical therapies that aim to improve survival or reduce morbidity kind of thing. If we come to the surgical portion, for example, the biggest, the number of cases, any place would mention they're getting is complicated monochronic twin procedures.

You have twins, we share placenta, monochorionic twins, and they end up with certain complications because of those unbalanced share in the vascular connections. Most commonly is twin-twin transfusion. The treatment is laser surgery, and that is done fetoscopically. It's minimally invasive approach. Then you can use the laser for other rare condition in the twins, such as twin anemia-polycythemia, such as really bad selective fetal growth restriction, you can do laser.

For monochronic twins, also sometimes you might do other things, not necessarily laser, such as selective reduction using bipolar, using radiofrequency ablation, using microwave thermal ablation. This is like for complicated twins. For spina bifida, we mentioned fetal surgery for spina bifida. For congenital diaphragmatic hernia, we mentioned the tracheal balloon occlusion. For any type of fetal anemia, whether that is from hemolytic disease, whether that's from parvovirus or some genetic anemia condition, we do intrauterine transfusions.

Then you have those conditions that you would require a shunt for. For example, you have lower urinary tract obstruction, or known as posterior urethral valve. We put a shunt into the bladder to bypass the blockage and drain the fluid into the amniotic fluid. You might have a pleural effusion, and then we put a shunt in the chest to drain the fluid to the amniotic fluid. Then you have a little bit more rare conditions, such as amniotic band. You have those amnions that wrap around different limbs, and they might cause amputation. It depends on certain eligibility.

We might offer resuction for those bands. You have a placental chorioangiomas. If they result into cardiac overload and poly, et cetera, we might offer laser or coils or just symptomatic intrauterine transfusion therapy kind of thing. This is an overlay of surgical procedures, and there's others that becomes a little bit more and more rare. When it comes to the medical portion, this is more of the innovative portion. It's like those are therapies that you do after the baby's born, but you're thinking as a fetal therapist, what if I started when the mom is still pregnant?

For example, Tony, you might be aware about the patient. The patient's story on was cystic fibrosis, in which we started the TRIKAFTA early when she was pregnant. The thought is it might reduce the bowel complications from the CF if we start the treatment early. The mom takes the pill, it goes transplacental to the baby. There was recently a case report that's published in The New England Journal, and our group is currently looking into possibly starting it as well, which is a pill medical therapy for spinal muscle atrophy, SMA.

That case report was published from St. Jude. We as a group, we already had a meeting with our SMA team, and considering of possibly if we found an eligible patient, it's maybe-- again, there's a lot of unknowns, but it's one of the therapies that's proposed, for example. Other things, such as sirolimus, which is an mTOR inhibitor that's been proposed out there for cardiac rhabdomyomas.

Similarly, it's a pill mom takes, goes transplacental to the baby, and so on and so on. It's medical therapy, yet it's very innovative, not much research, not much data, but there are registries out there that people try to put those data on, and hopefully, we have more clarity in a few years ahead kind of thing.

[Dr. Anthony Shanks]
When I trained, we were doing amnio reductions for these TTTS cases, which temporizes things, but doesn't get to the root of the problem. Then the paper came out about using laser therapy. Pretend you're talking to a student that has not seen that video and knows what you do. Briefly take us, when you say laser therapy, what does it actually entail?

[Dr. Hiba Mustafa]
Basically, we call it fetoscopic laser coagulation, so that's the name. We use fetoscopy, which are instruments just like laparoscopy. When it comes to the fetal procedures, those entry points that you do, whatever entry point you make using your needle or instrument, it was found by animal studies and in vitro studies they don't heal. The amniotic membrane don't have a healing capacity. We always aim in using smaller and smaller instruments. Although it looks like laparoscopy is not as big.

The biggest fetoscopic may be like a four millimeter kind of thing. We use different entry technique. We call it percutaneous. Percutaneous meaning the skin to uterus to inside the uterus. It's like one entry through the skin all the way into the amniotic sac. That's what percutaneous means. As I said, different sizes. It depends on different things. Generally, four millimeter is the biggest size. Through that scope there's like different channels. One of them, you can add amniotic fluid or draw amniotic fluid.

There's a special channel for like a laser fiber, which is a very thin laser fiber kind of thing that you can pass it through that special channel in your fetus scope and you go. It's a very small camera. People think like we can have like a very nice panoramic view. "Can you take a picture for the whole baby?" "No, I can't take a picture for the whole baby." It's like a very small pointy camera. The most place you can see is actually what you're literally looking at kind of thing. It doesn't give you a panoramic view.

We use zero and 30 degrees, but even with 30 degrees, you can't really have much of a view. Before going in very, very important is we know what we call equator. Equator is that line. It could be like regular line. It's not a straight line. It's just a line curved, whatever it is of those vascular connections between both twins. You have to have a good understanding where your equator would be to end up being 90 degree against your equator. Otherwise, you cannot just go in. "Oh, this is not a nice spot. Let me go out and go another entry."

That's not good because she's going to just deliver and break her water. Have a peep around, so the entry point you decide on should be it, and you should have very good idea of where to enter. That is generally should be almost 90 degree against your equator, which is that line in which the connections would be. That line is determined by where is the placental cord insertion of each twin. If you have one cord insertion here, one cord insertion here, left and right, the equator would be the line between two cord insertions kind of thing.

If you know the line, you look at the mom's abdomen. We always go into the sac that has polyhydramnia. That's the recipient sac. We don't go to the sac that doesn't have a fluid. We end up into the recipient sac, 90 degree against the equator, and we try find these vessels, pass the laser fiber, burn them. Then the trial that came, which is the Solomon, basically, they found that if you burn in between your burning points, like we call it dichorianization, meaning you create two placentas kind of thing.

They found that it reduces recurrent TTTS and TAPS after the laser, because TAPS, you can have those very hair-thin vessels that you can't actually see them really well. That's why we burn in between our burning points, what's called Solomonization kind of thing. That's in brief what we aim to do during laser surgeries.