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This episode is brought to you by Prime Obsession is in session. And this summer, Prime Originals have everything you want. Steamy romances, irresistible love stories, and the book to screen favorites you've already read twice off campus Elle every year. After the Love Hypothesis, Sterling Point and more slow burns, second chances chemistry you can feel through the screen. Your next obsession is waiting. Watch only on Prime.
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Podcast Family. Without you guys being our listener support system, without the great questions that come in, me and Michael will just stare at each other and our marketing team would have nothing to do. So thank you for these great questions that come in, like this one from Serena.
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Hey, Dr. Chapa, we love your show. I listened to your episode on Lust for C Section. I understand that we don't need to measure the lower uterine segment for TOLAC approval, but what if I see a super thin layer there, like a scar window that needs a repeat C section, right?
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So if you don't remember what that means, Lust for C section, go back in our archives and take a look at that. We'll put the show notes, the link to that episode in our show notes. But we covered Lust for C Section, and I don't mean that in a creepy kind of weird way. Lust for C section stands for lower uterine segment thickness. Okay, Lower uterine segment thickness. In other words, do we need to measure the lower uterine segment before a patient with a prior C section is allowed to toe lack? You got to go back and listen to that short answer is. It's complicated. And while the data looks promising that a very thin lower uterine segment could be a risk for rupture, that is in the ACOG or SMFM or international standards for the allowance of tolac. All right, well, I guess I told you anyway. I was going to tell you. I was going to say that I was going to give you the specifics, but, well, there it is anyway. Lust for C section, lower uterine segment thickness. And the reason that ACOG doesn't use that is because there's a lot of heterogeneity in the studies. And we'll get into the main factor here right after the intro. However, even though, as Serena very well stated here, even though we know that we don't have to measure that and we should be looking, remember, guys, for any patient with a prior C section, even if they are cleared for toe lack, you should look at that lower uterine segment specifically to see where the placenta is to make sure that there's no PAS placenta creta spectrum. So you've Got to look. Where's the placenta and is it away from the incision site? So we should always be looking at the lower uterine segment. However, routinely measuring it for toe like clearance is a lot more gray and complicated. Go back and listen to the episode titled Less for C section. However, as a caveat, what if you're looking down there and you're like, oh, well, that's interesting. It's like very, very thin. And in the rest of Serena's message, it actually states it's like less than 2 millimeters. That's really, really thin. What do we do with that? Well, again, it's a complicated question, but there is an evidence based answer that has to do more with standard of care than evidence guidance. Remember, we've talked about this recently in past episodes where standard of care is what a reasonable physician would do in the community and you would think, and the vast majority of the time it is true that goes with evidence based data. But sometimes evidence based data base data goes to one direction, like west, and community standards go the other direction, like east, all in the name of patient protection. So I guess you may be getting a feel of where I'm going here. So we're going to talk about if you find a window at time of antenatal ultrasound. Hey, just doing routine ultrasound. You're like, oh, lo and behold. Well, that's not good. I mean, it's super thin in the area of the old C section scarlet. And we know it's not going to get any thicker because it's not going to grow tissue there. Miraculously, it's going to get thinner as the lower uterine segment further develops. Should we allow this patient to tolac? Very good question, Sharina. It's super complicated. I think I've set it up enough. Let's get into this issue of a window at routine ultrasound and what to do. We'll be right back. We're just trying to fulfill our life calling and our mission. This is Dr. Chapa's OB GYN no Spin podcast. All right, Podcast family. I wasn't gonna do this, but it leaves me no choice. So just so you understand the kind of abuse that I get here from my own team, AKA Michael, our producer, our marketing girls, they. They kind of stayed out. They did do their own deal, but Michael keeps me honest. And this time he was right. So we finished the intro and. And he said, hey, you said something wrong. I'm like, what? Look, look, man, he's not even medical, all right? He's media. And it's I'm like, what did I say wrong? I mean, I've got my notes. Everything is like, triple cross checked. What did I say wrong? And yes, lo and behold, I gave you the wrong name of our previous episode. I said it was Lust for C Section. Sorry, Michael was correct. It is Lust for Tolac. That was at the end of December, end of the year 2023. And then we actually had a follow up in mid January of 2024. So I've got two episodes on Lust for Tolac. Sorry, not Lust for C Section. And I told. When we were off the mic, I said, michael, I'm going to tell him that you were correct. And he said, oh, man, you're being such a baby. And I'm not a baby. I just. When I'm wrong, I. Oh, my God. All right, stop it. No, it's not being a baby. Sorry. Stop it, stop it. It's not being a baby. It's being. I. I'm owning up to my air. You know what, man? You're gonna be fired. No, I can't fire him because I want to take an open call edition for media producers next. Stop it. So let's get into this. Let's get into the data now. My goodness, what were we talking about? Lust. Lust for Tolac. Right? So low urine segments. So very quickly, guys, let's get over this very quick. I don't want to belabor this, but what a great question. If you're doing a routine ultrasound looking for where the placenta is. Like in this case, it was anterior, more anterior fundal, definitely not anterior, lower uterine segment. But Serena said, wow. Well, there's like a window here. I mean, what she measured was at the thickest 2 millimeters. So just so you know, that's pretty darn thin. Okay, but that is one of the issues here, that's an inherent problem, is that we really don't have a true definition of what is considered thin for tolac. And that's why ACOG and SMFM and even some international societies don't include that measurement. But everybody can pretty much agree that at 2 millimeters or less, universally, that's just thin. I mean, some say 2.5, some say 3. Some measure the entire thickness from serosa on the outside all the way to the inner basalis layer. But the truth is, you should really just measure the inner area that looks a little bit different. You got to bring that up, magnify that up on your ultrasound. Have a good resolution ultrasound, and you can actually measure just the myometrium. And a myometrium that is less than or equal to 1.5 millimeters, based on the data, that's kind of a flag. Okay, that does raise the risk of rupture. The problem is that the relative risk is still pretty low. In other words, it has a very high negative predicted value. So if it's thick, it reduces the risk of rupture, but if it's thin, it. The positive predictive value is very low. Okay, so a thick, lower uterine segment has a good and sturdy negative predictive value, but the positive predictive value, meaning that you really will rupture, is like at most 8%. Now, 8% is high, but that means that 92% of the time you're going to be wrong. Okay? And there's a reason for this, is that what you see sonographically doesn't always translate to what is seen clinically. That's why we don't look for this. I mean, our group doesn't do it outside of looking at the load segment for placental attachment. And if we see some weird, you know, varicosities or PAs, that's a different issue. But just because it's thin, we take that on a case by case basis and that becomes. You all get it, guys, three words, shared decision making. And that goes into good documentation. But we got to be very clear because on the one hand, we have clear guidance here and that acog, smfm, international societies do not include a thickness measurement right now as an exclusion criteria for tolac. It is the typical number of C sections, type of uterine incision, any contraindication to a vaginal birth, you know, like a vasoprevia or a regular placenta previa, herpes infection, whatever, that would make vaginal labor and vaginal birth not a good idea. But nowhere in that risk stratification or risk calculator does it have low uterine segment. However. However, it is a problem. And it's one of these things of, you know, if you don't look well, you didn't measure it, you just don't know. But if you do know and you see that it's super thin and then she ruptures, it could have been a preventable issue. So here's where there's this disconnect between what's then in the community, because I'm going to give you proof. Proof, guys, based on data that most of the physicians, when they see a very thin low uterine segment, will actually choose a repeat C section, which is why the rates of Rupture are extremely low because you've kind of. That's called cohort bias. You kind of change that study population. But most would absolutely, based on community standards, say, I'm not comfortable with this. You can do whatever you want to do because you're the patient. We'll call that shared decision making. But my recommendation is that there's too much to gamble and lose here on the roll of the dice. So we're going to be out. I'm going to give you that data because that's actually published. That was published in 2016 by Jastow et al. Okay. Just actually there's an R in there. Sorry, Gastro, G A S T R O W Gastro et al in the gray journal. Okay. So most would absolutely section that even though ACOG says the positive value is unclear and it is of unproven clinical significance because we're likely going to over call that. So before I give you the data, if you can't figure out where I'm going, while it is not an absolute indication for C section, be very clear that a CNA window is not an absolute indication for C section. However, it is the community standard to do so. In other words, that become standard to practice versus an evidence based guidance. All right, this is very similar to what we've talked about in the past. We've talked about like home blood pressure monitoring and obstetrics, where that is a community standard and, and that is referenced by the college, by ACOG as something to do ambulatory blood pressure measurements. Even though the data with bump one and bump two is disappointing, you see, sometimes evidence based guidance, evidence based data, evidence based facts don't move in the same direction as community based standard of care. Is that phenomenal or what? Okay, so let me give you this study by Gastro et al published in ajog and then we're going to be done. So they followed close to 1900 women with previous C section and then they measured their low uterine segment at around 34 or 38 weeks. And then they gave them three different labels. Okay. They gave them their tag. Here's your tag. There was either a red tag. It's like that's high risk for rupture. That means that it was an extremely thin lower uterine segment. Based on their protocol, they gave him a yellow tag which was an intermediate risk and then they had a green tag. Now guys, they didn't really give them tags. I'm just trying to make it easy. Give us a mental picture. All right. They were deemed as either High risk, intermediate risk, or low risk. And the low risk had a nice thick lower uterine segment. Okay, so to be clear, no, they didn't really give them tags. I'm trying to make it user friendly, but they did give them those three classifications based on the measurement of their low uterine segment. So look at this. Those that were deemed low risk, 61% of those attempted TOLAC. Okay, more than half. That's reasonable. The intermediate risk, 42% attempted TOLAC. You get that? So it's a little thinner. You're like, makes me uncomfortable. But still an option. Those that were deemed high risk where they saw a extremely thin lower uterine segment or AKA a window, just like Serena's talking about here. Listen to this. Only 9% attempted a TOLAC, meaning 91% resulted in a repeat section. Okay? Now these did not attempt tolac. So I have proof that in the community, most people who see a window are like, man, I can't put you in harm's way. The thing is, I looked for it, I saw it, and if I hadn't seen it, maybe things would have been fine. But now I see it, and I can't let you do something that potentially would be harmful that goes against primum non seti. Okay, so first, do no harm. So do you all get this? Is that fascinating or what? So now, oddly, that's cued your entire results because the rate of uterine rupture dropped to basically zero because they took out everybody who was high risk. So they said, hey, see, there's value here. If we take out those that are really scary, you can drop your risk of uterine rupture down to zero. Yeah, but who knows if that would have still been zero if they were allowed to labor anyway? Because the positive predictive value of this based on some published studies is on a good day, maybe like 8%. Okay, so fascinating stuff. So let me just start to wrap this up and then we'll be done. So here's take home message. While no major guideline explicitly lists a uterine window as an absolute contraindication of tolac, that finding is generally regarded in the medical community as a significant risk factor for uterine rupture. That should prompt clinicians to at least an evidence based discussion and shared decision making with the patient to favor against TOLAC and in favor of a repeat section. Now, we have one of these patients in our group right now. We just got the report back from our sonographer and like, oh, well, isn't that interesting? She's got like, you know, one cell layer between the child in the amniotic sacrifice and her perineal fluid. I mean, it was like, you know, one cell grabbing one end and grabbing the other end going, I'm staying together here. It was like, I don't know, whatever it was, one millimeter. I'm not going to let her labor. I'm just not going to do it. But that's how I documented it. While no professional society says I can't do this, and unless the patient feels very strongly where I work for her and I will do whatever she wants to do, she's part of patient autonomy. But it's my job to give her the information that that is a risk factor for rupture. However, that risk factor is controversial. I can't tell you how high it's risk factor because the positive predictive value is very low. And it's something, though, that if we're wrong, it could be catastrophic. So this is where the harm is so high from rupture versus an elective repeat section where the risk imbalance ratio here shifted towards a repeat section. But I document all of that and I tell the patient, no, again, have I labored these patients who don't want to repeat section? Of course, and they've been fine. However, our index of our threshold of patients intrapartum is also significantly lower. So at the first chance that she gets stuck, then we are out. You see how knowing that influences even labor during tolac intrapartum. Because you should have. And that's the right thing to do. You should have a lower threshold of patients. In those patients, they're already starting with a leg cramp as they run their marathon, so to speak. Okay, so in clinical practice, the discovery of a uterine window on ultrasound in a patient with a previous C section should definitely prompt counseling and according to consensus opinion and expert reports and commentaries, should probably favor a repeat cesarean delivery. Even though we have no call to measure the low uterine segment, if you see something in, you can't necessarily ignore it either. Podcast family, as always, we're thankful for you. We're glad you're part of our podcast community. Michael. Was that enough of a baby for you? Was that. Are you happy now? After you. Is that good? There you go. I knew you were gonna do it. I knew I knew it. Do I know you, brother, or what? I saw the finger go ready on the push button. Oh, Lord. You see what I have to work with. Podcast family. Be on the lookout for an Instagram post for a new hire for a largely popular ob GYN podcast. All right, Michael, don't you go anywhere. Podcast family, as always, we're thankful for you. We're glad you're part of our podcast community. And now that we've done all that, let's take it home. This is Dr. Chapma's obgyn no spin podcast.