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- [00:09]
A
You didn't prepare me for a big, giant fat baby.
- [00:12]
B
Well, there's probably better ways of saying you have a big giant fat baby, like saying babies large for gestational age. Or of course, macrosomia, which is a set fetal weight above a certain cutoff. Traditionally more than 4,000 grams. But big baby, yeah, they are definitely out there, you big baby. The question is, what do we do with a big fat baby in utero as we get to term? Now, of course, let's set the stage. Currently, as of today's date, neither the ACOG nor SMFM currently support routine early induction of labor for suspected fetal macrosomia. Of course, instead, they make the rules, the guidance, that at certain set cutoffs, with or without the presence of diabetes, the patient should be offered a cesarean section as part of shared decision making. So it's 5,000 grams or more without diabetes for the offering of a C section and then 4,500 grams with diabetes for the offering of a C section. Although several hospitals and different institutions have their own policies, some use a fetal weight of less than that at 4 to 50 grams, 4250. But that's part of their internal policies in general. General, though, it's 5,000 grams and 4,500 grams, again without or with diabetes for primary cesarean section offering. So, as of right now, ACOG's current guidance and SMFM does not support routine early induction for LGA macrosomia. Okay, that's not a thing. However. However, there was a trial in 2025 which was very large. It was multicenter, it was open label randomized, and this was PUB into Lancet and it was appropriately called the Big Baby trial. Big Baby. This trial looked at whether early induction, like 38 to 38 and a half weeks versus expected management, was better in terms of shoulder dystocia reduction or prevention. Okay, so this study had a one to one randomization. It was very well done. It was actually through the NHS system and included England, Scotland and Wales. And if you just read the commentaries of this, without actually doing a deep dive into the data, you get something like this quote. The per protocol analysis demonstrated a significant reduction, 40% in fact, in shoulder dystocia with induction of labor at 38 to 38 and four days, as opposed to expected management, 40% reduction in shoulder dystocia. I'm in, right? I mean, who wouldn't want that 40% reduction? However, the key there is what was said in the first part of that sentence, the per protocol analysis. So this is a Great example, guys. And what we're covering this is because even though this happened in the second part or the mid part, I guess, of 2025, and we're doing this now for two reasons. Number one, we got a recent question on this just after the start of the new year from one of our podcast family members asking about this, which said, hey, isn't the big baby trial a pretty big thing? And isn't that kind of going against ACOG's current guidance of not offering early induction based on fetal weight? And what do we do with this big baby trial? And so I thought, you know what, I saw this when it came out in around May of 2025. We said, Ah, it's, it's, it's just not worth it right now because the guidance really is very clear on this. But this question came in and it made it, and it made me think about the real importance here, guys, of reading the entire study, because it's very clear when you read the study, what was shown in the intent to treat analysis versus what was shown in the PER protocol. Because in one, the PER protocol, 40% reduction in the rate of shoulder dystocia. And number one, you have to ask, well, what was the absolute number? We'll get into to that. And the second is, well, what was the difference in the intent to treat? And the truth is there was no reduction in shoulder dystocia in the intent to treat. So the question is this, what does that mean? Should we look at the per protocol result or the intent to treat? And what do we do with this big baby trial? Which, thankfully was very large, very well done. But it does explain why currently ACOG and SMFM have not change their recommendations about early induction even when there is a big old fat baby in utero.
- [05:08]
A
You didn't prepare me for a big, giant fat baby.
- [05:11]
B
Yep. So in this protocol, we're going to figure out, in this episode, rather, we're going to figure out the per protocol and the intent to treat differences, why they actually matter. And we're going to explain why itt, in a randomized trial, intent to treat actually is the more reliable conclusion and findings over the per protocol, although per protocol still is. Okay, it kind of mimics, quote, unquote, real world issues, end quote. Although the real world issues have something that cannot be verifiable in the data. In other words, it makes the data muddy, and that is selection bias. So the big baby trial, you big baby. Yep, that's what we're gonna talk about in this episode. What do we do with the big baby trial. Do we induce early for suspected macrosomia LGA, or follow the current agog and SMFM guidance? I think I've set it up enough. We'll be right back. This is Dr. Chapa's obgyn no spin podcast. All right, if you know me at all, you know I am kind of a geek fan of the office. Michael, one more time. We just got to hear one more time and then we'll get to it. To it.
- [07:09]
A
You didn't prepare me for a big, giant, fat baby.
- [07:13]
B
All right, Anyway, so, yes, this is a big deal because we do fear the big fat baby in utero because of shoulder dystocia. Even though, if you read the guidance, most babies that get shoulder dystocia are not, you know, over the 4,000 macrosomic, even though they have a higher relative risk because most babies are not macrosomic, they're actually under that. And that's why shoulder dystocia is still relatively unpredictable, slash unpreventable, according to the guidance. Okay, now there's risk stratification, and we absolutely should do that. But as of right now, remember that neither ACOG nor SMFM does recommend early induction just because of the baby's weight. And that was covered in Practice Bulletin 178. Okay, that's the one on shoulder dystocia. Now, in that guidance, there's a very little, short, little paragraph. Well, it's not short, but a short section rather. On quote, is there any benefit to labor induction for the prevention of shoulder dystocia in the setting of suspected macrosomia or diabetes? End quote. That's the question raised. I'm reading that directly. I'm looking at it right now. 178. Is there any benefit to labor induction for the prevention of shoulder dystocia in the setting of suspected macrosomia or diabetes? End quote. Notice I highlighted and emphasized the word macrosomia. Now, this is a big deal here because whenever ACOG really talks about shoulder dystocia, even though it recognizes that not all babies with shoulder dystocia end up being macrosomic, they can be LGA. The guidance here is more clear on true macrosomia. 4000 grams or above. Okay, so keep that in mind, because a big baby trial wasn't really looking for macrosomia. It was including babies that were suspected of being lga. You understand that those are loosely associated but very different. So that all babies that are macrosomic are lga, but not all LGA babies are Macrosomic, Right? Because larger gestational age is greater than 90 percentile. Estimated fetal weight on ultrasound based on the week of gestation. So that you can have a 3.6 kilo baby be LGA at, you know, let's say, you know, 36 weeks. But not macrosomic. Because macrosomia is a set line. It's a boundary. It's a line in the sand of when you cross 4,000 grams, you're not macrosomic. All right? So keep that in mind. Right now, the college focuses more on macrosomia, whereas Big Baby said the Big Baby trial was more on LGA. Okay, now back to 178. And ACOG's answering this question. Is there any benefit to labor induction to prevent shoulder dystocia? Let me just read this directly, okay? Because the short answer is no. Quote, the American College of Obstetricians and Gynecologists recommends against delivery before 39 completed weeks of gestation, if not medically indicated. Whether induction is better than expected management for suspected lga. See, there it is. And at what gestational age delivery should be performed remains unclear. End quote. So let's stop there for a minute. So there they introduce the topic of lga. You're like, we don't know. We get macrosomia where we get the cutoffs of 5,000 grams without diabetes off resection, 4,500 grams with diabetes off resection. But we don't really know what's the best LGA determination and how many weeks to get out for shoulder dystia prevention. So that's where people get confused. Like, ah, well, the Big Baby trial looked at LGA and it answered that yes and no. Because the per protocol answer was one thing, the ITT answer was another. Remember, we're gonna get into short of it is the college continues. Although meta analyses of available trials is provocative and raises questions for further study, it is not clear that the reduction in shoulder dystocia found in the included trials would still persist if labor was induced after 39 weeks of gestation at this time. This is from the college. And until the results of additional studies are reported, the ACOG continues to discourage induction of labor and solely for suspected macrosomia at any gestational age, end quote. So that's the guidance as it stands now. Okay, now, yes, practice bulletin 178 is was originally done some years ago. However, it was. It's been re. Reaffirmed since that. So it's still valid. Okay, remember, that is the guidance on shoulder dystocia it was actually reaffirmed in 2024. Okay, reaffirmed 2024. Okay. So back to what we're talking about. So right now, college says, no, we need more data, especially with LGA because it gets very gray in the lancet. On May 17, 2025, the Big Baby trial was published. And that's what our podcast family member was asking about. The truth is, this was a big study. It had a big data source. It was good. Okay? It was very well done. And it looked at induction of labor for LGA babies, specifically looking at 38 to 38. Four for the reduction, shoulder dystocia versus expectant management. And sure enough, 40% reduction compared to standard care, which was delivery at or after 39 weeks in the per protocol. Per protocol. However, in the intent to treat analysis, there was no statistical significant difference. Okay, so let me. We're going to explain this here in a minute, by the way. Sorry, guys, I still have one nostril working. If you listen to the immediately passed episode, I'm working through my annual viral syndrome nos and much better now, but, you know, my respiration still come and go. Okay, anyway, so 40% sounds really good, especially when you consider that this had one of the largest, you know, patient recruitments to look at this, that used LGA as their. As a recruitment pool. Okay? So once again, let me give you what these actual numbers look like. So in the per protocol analysis, 40% reduction looks like this. 2.3% in the induction group for shoulder dystocia, 2.3 versus 3.7 in the standard care group. So again, 40% reduction is great, but, you know, 2.3 is definitely less than 3.7. Now take any reduction, but it's not. It's 40%. Again, good, but you have to understand what per protocol means. Per protocol means that even though the original two groups standard induction at 38 weeks, or standard induction or routine care at 39 weeks, even though they were randomized, some physicians and or patients left one group to go into the early induction because clinicians were afraid they broke protocol. Okay? And so they got. They left the intended design of the study called intent to treat, and then they bailed. So when you look at the per group, which includes those that were taken out of their randomized original trial and were added to this one, yes, it showed a reduction in shoulder association. That's great. However, the big catch here is that you lose the validity of the data of the randomization. The whole point of randomization is that you try to limit chance Right. And bias. So when you look at the PER protocol and go, wow, there was a reduction in shoulder dystocia. Great. However, it's not clear data, because that has the biggest issue here is selection bias. That, my friends, is the catch. The intent to treat analysis in itt. When most randomized trials have an ITT and a PER protocol, the ITT analysis preserves the benefits of randomization and it keeps the prognostic factor, in other words, the validity, accuracy of the data more pure. So in short, we should be more inclined to believe the scientific validity of intent to treat results. And in this one there was no statistical difference. Difference. Although PER protocol does mimic more real world, real world stuff in terms of statistics is muddied and confounded by selection bias. Okay, so all to say, intent to treat results are generally considered more reliable than per protocol results in randomized trials. And this is why in the big Baby study, the intent to treat pool found no difference. Which means what we probably saw as in that 40% reduction in shoulder dystocia 38 to 38 and four weeks was part of selection bias. Okay, now here's the other catch. Are you telling me that induction at 38 and four days gave a reduction in shoulder dystocia compared to 39 weeks in three days? I mean, we're talking about baby grazer grows about 30 grams a day, guys. That term, 30 grams a day. So you're telling me that the 90 grams difference prevented shoulder dosha? Doesn't make any sense. Even at 38 or 39 weeks, if we get out at 38, that additional week of baby's growth, baby grows half a pound a week. That's about 250 grams. Is 250 grams gonna be enough to push a baby over into shoulder dystocia? I don't know, it doesn't seem to be so. And that's what ACOG mentioned in that guidance. We're not sure at what EGA is valid. And even though meta analysis seemed to show this reduction, quote, it is unclear if the reduction in shoulder dystocia would have been still persistent if induction was found at 39 weeks. That's exactly what's in the guidance. In other words, we're not talking about a three week induction here earlier, guys, we're talking about a week. And in a week's growth, yes, baby is bigger a week later, assuming the placenta is functioning well. But the baby grows half a pound a week by grams, that's about, you know, 220, 250 grams this year. So 225 to 250 grams. Unclear if that's really going to move the needle all the way to shoulder dystocia. Guys. And I'm not minimizing the big baby trial, but the reason we didn't cover it initially is because, you know, when we first saw this come out in the Lancet, I told the team, they're like, well, do you want to do it? Is it confusing? I'm like, you know what, we already have clear guidance on this. We don't induce judge for that. We look for other reasons. I'm okay, I'm all for looking for other reasons to deliver. You suspect LGA look for other reasons to get out, but LGA by itself, really, as of right now, is not it. And this study actually verifies that per protocol. 40% reduction. Yes, I get that. But the intent to treat, which is pure data, did not actually show any significance, by the way. It's not just me. I'm not the only one saying this. There was actually a, a published commentary on this shortly after the, the published paper was released. And, and here's what we're going to give you with the three main, the three main limitations for this, we're going to call it a day. Okay? And again, I'll put the all of this in our show notes, but there's a very nice correspondence as a letter to the editor about this, which hit it exactly the nail on the head, which is what I'm trying to say here. First, limitation number one. The premature termination of the trial and crossover between the two study groups left little statistical power in the standard group compared to the induction group with a confidence interval that crossed one. So there it is right away. Confidence interval in this was 0.5 to 1.09. So while it was tight, the confidence interval crossed 1 and the P value was not significant in the intent to treat group. Okay, so they stopped the trial early. There was too many people leaving one group going into the early induction group, so the data is muddied. Number two, rather than using straight macrosomia, they use this looser eligibility, which we've already said of an estimated feet of weight above the ninth percentile, which is called, you know, lga, which actually doubled the estimated risk unnecessarily. In other words, if you just broaden the net to lga, it's gonna give you good capture. But most of your specificity in the data is with true macrosomia. And so this is why the actual birth weight mean in the control birth weight here was 3,857 grams, as opposed to a true macrosomia over 4,000 grams, which, again, you're not sure what to do with this. Even ACOG says not sure what to do with LGA versus true macrosomia number three, only 40%. Listen to this, guys. Only 40% of the participants deemed at high risk actually had the infant who was LGA at birth. In other words, when they weighed the child, like, hey, this kid's under 90th percentile, which means, quote, there was a 50% predictive value of late ultrasound for accuracy for fetal weight, end quote. This is what ACOG says. Ultrasound is good, it's just not great. And there's a lot of variance in there, up to 15, up to 20%. Room for error based on who you read. So in this study, 40% of those who were thought to be high risk for shoulder dystocia actually birthed an infant that was LGA, mirroring the 50% predictive value of late ultrasound. So all to say again, as ACOG says, this is why the bar is so high for offering a primary C section without diabetes of 5,000 grams, because ultrasound just has an inherent inaccuracy. And it's more inaccurate as gestation progresses, both for dating and for weight assessment. And that's why the values are for 5,000 grams without diabetes or 4.5 kilos, 4,500 grams with diabetes. Okay, now, before we leave the episode, I want to quote directly from this commentary again from the Lancet, published in October 2025. Remember, the original article came out in May of 2025, and then in October, actually, October 11, 2025, this commentary, which again, hit it right on the head, covers it beautifully. Let me just read you this last little statement here, this little paragraph, and we'll start wrapping this up. Quote, guideline committees, AKA smfm, nice guidelines, rcog, smfm, acog, whatever. Guideline committees should now consider whether to spend substantial resources. Uh. Oh, see, so it already starts off kind of negatively, Right? Guideline committee should now consider whether to spend substantial resources to recommend induction of labor in these patients. For. I'm reading it directly. Modest benefit. Okay? Not great benefit. Modest benefit given uncertain case findings, period. So right in the first sentence is like, hey, we're unsure. Committees are got to be really sure if they're going to change guidance based on this because, quote, it has uncertain case findings, then, quote, they go on, quote, until better tools become available, nuanced counseling is the most promising strategy. Women with a fetus above the 90th percentile might await labor, whereas those with a fetus above the 95th percentile or greater or a birth weight above 4,500 grams or a previous shoulder dystocia or rising morbidity might choose induction or elective cesarean. So in this last paragraph it says, hey, just pump the brakes here. We need better data, we need less crossover, we need trials to not finish early. Because it's unclear these uncertain case findings before we change, guidance here may be a way to cleaner data. Okay, that's all they're saying. So my take home message as we get ready to wrap this up again, look for a reason if you're really worried about it, under 39 weeks that you can medically be cleared to get out. And patient history is one thing. The second issue has to do with 39 weeks. If you suspect baby is LGA, but below the cutoffs for offering a primary section, why would you go past 39 weeks at 39 weeks with good dating, you don't even need a reason. That's elective induction. Assuming the cervix is favorable and the patient accepts risks. All to say induction early just for suspected fetal weight is more complicated than the 40% reduction found in the per protocol analysis from a study that found no statistical difference in shoulder dystocia in the intent to treat. So I think I've said that enough. Let's get ready to start wrapping this up. But anyway, that was the correspondence from October 11, 2025 in the same journal the lance it so to our podcast family member that asked about the big baby trial. Yes, it was very significant. However, there was a lot of crossover, the end of the trial early, their selection bias and so here's my take home message. I look for things at 38 weeks if I think this kid is ginormous yet under let me just back phrase that, backpedal that a little bit under the cutoffs but I am worried. Then I look for other things. Is she dilated early? She in latent phase? Is her blood pressure issues, anything else that can give us a medical justification to get out now, all with the patient's history. Guys, if she's had three previous shoulder dystocias, why has she had three? That's the first question. I'm just making this for point of emphasis because the biggest history of shoulder dystocia. The biggest history, the biggest risk for shoulder dystocia, while big baby is one. It's a previous history of shoulder dystocia that complicates matters.
- [25:16]
A
You didn't prepare me for a big, giant fat baby.
- [25:20]
B
So if we're prepared for a big, giant fat baby, then we should offer the patient appropriate consult with the patient's history first and foremost in our mind. Okay, so the big baby trial. Lancet, May of 2025. Great question from our podcast family member. This is the difference between per protocol and an intent to treat. Per protocol was intriguing. It's provocative. 40% decrease. But there's selection bias in there. Plus the recruitment of LGA versus trait macrosomia and the fact that the positive predictive value of fetal LGA on ultrasound was only 50%. It's just. It's unclear here. So don't ignore a large baby. Please don't ignore a large baby. But again, routine induction just for this doesn't seem to be the issue either. Doesn't seem to be the answer either, Michael, One last time. Then we'll call it a day.
- [26:15]
A
You didn't prepare me for a big, giant fat baby.
- [26:18]
B
Yep, we all have to prepare for a big, giant fat baby. But maybe as of now. Maybe as of now, early induction at 38 weeks doesn't seem to be the answer. All right, podcast family. I hope I did this justice to our podcast family member. Thank you for sending in that question. Short answer is selection bias per protocol versus ITT. And current guidance, as of now reaffirmed in 2024, does not show any reduction in shoulder dystocia with early induction. 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 has been Dr. Chapa Zobichyn, no Spin podcast podcast family. Thank you for your support. Thank you for listening. And as always, we'll see you on another episode of the no Spin podcast Cast.