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C
Yes. Oh yes. In your face. In your face. What annoying thing is happening now? They're playing Diagnosis Jeopardy. When you win, you get to gloat. It's so stupid. So there is a reality that we kind of do stupid things sometimes as medical students, as residents, even as attendings. Like Medical Jeopardy. Well, well, that was out of Scrubs, not a sponsor. But the idea is sometimes it's good to just rehash some diagnostic issue or dilemma because it's actually a good learning case. That's what we're going to tackle in this episode. We're going to talk about the isolated finding of a fetal abdominal circumference greater than the 90th percentile. Now, let me clarify here. This is assuming that the normal view shows a normal anatomy, normal structures. All right. We published, I think it was in 2016 or 2017 where a patient presented like I think she was 34 or 35 weeks with absent fetal movement. The baby looked flat on the monitor. Of course. We put on an ultrasound to try to find a maximal vertical pocket and lo and behold, we didn't see diaphragmatic excursion and the abdomen was almost filled solid tragically, with this echogenic just, you know, mass. It ended up being, of course, a very large liver that was full of metastases because the fetus in utero had metastatic neuroblastoma. We published that when she presented as decreased fetal movement. So tragic. So for this episode and what we're trying to set up here, let's assume that the abdominal circumference is greater than 90 percentile, as it was in that example I just gave you. However, the abdominal contents looks normal. All right, so let's exclude anything, you know, odd and rare going on. Just an isolated abdominal circumference. Anatomy is otherwise normal. All the other parameters are less than 90. But the fetal abdominal circum is greater than 90. What is the diagnosis? So we're gonna talk about what is a diagnosis here. Now, let me flip the script here. We know that an isolated abdominal circumference under 10th percentile as an isolated finding is good enough for fetal growth restriction. You don't have to have the composite EFW all be under 10%, even though that also is a diagnosis of FGR. But just the isolated abdominal circumference under 10% by itself is diagnostic of FGR. So is the rebuttal true? Is the opposite end of the spectrum true? If the abdominal circumference is greater than 90%, then is it possible that that is diagnostic of LGA? Yes. Oh, yes. In your face. In your face. What annoying thing is happening now? They're playing Diagnosis Jeopardy. When you win, you get to gloat. It's so stupid. So that's what we're going to do. If you got that right, if you know the answer and you get it right, you get to gloat a little bit. But that's what we're going to tackle. What is a diagnosis for an isolated abdominal circumference greater than 90th percentile? What is the diagnosis? What is the diagnosis? Oh, my goodness. All right, I think I've set it up enough. We'll be right back. This is Dr. Chapman's OB GYN. No Spin podcast. What is the diagnosis? So it is true. An isolated abdominal circumference under 10th percentile. According to AIUM, ACOG and SMFM and the UK's NICE guidance, everybody agrees under 10th percentile is diagnostic of fetal growth restriction. Because the abdomen is the first to show signs of fetal growth restriction as glycogen stores in the liver, which makes up the majority of the fetal abdomen, become less than the abdomen first becomes 10 percentile. That's why you get a diagnosis. They get umbilical artery dopplers, they get surveillance, and then you have to follow the trends in weight to see if the entire EFW will drop then under the 10th percentile. Remember, we've covered this recently that although the abdominal Circumference of under 10 percentile is diagnostic, you don't base management based on The AC by itself, you do get surveillance, you do get umbilical artery dopplers, but delivery is based on the total efw. Okay, so that's where it gets a little confusing. So the abdomen is very sensitive, but it's not the most specific. That's why you've got to look at the EFW to make delivery decisions as well as umbilical artery doppler findings. All right, so the question is, and it's logical, well, if a small abdomen is fgr, then a big abdomen is lga. It makes total sense. So logistically that's correct. The problem is diagnostically that is not correct. So right now, as Of April of 2026, the national and international consensus is that you cannot diagnose fetal LGA simply based on an isolated AC of greater than 90th percentile. If the EFW is under 90th percentile by Hadlock or whatever other composite formula you use. The majority of us uses Hadlock. We've talked about that in the past as well.
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Eczema is unpredictable, but you can flare less with epglis, a once monthly treatment for moderate to severe eczema after an initial four month or longer dosing phase. About four in ten people taking ECGLIS achieved itch relief in clear or almost clear skin at 16 weeks. And most of those people maintain skin that's still more clear at one year with monthly dosing.
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Hemglus Lubrication Asumab LBKZ a 250mg per 2ml injection is a prescription medicine used to treat adults and children 12 years of age and older who weigh at least 88 pounds or 40 kilograms with moderate to severe eczema, also called atopic dermatitis, that is not well controlled with prescription therapies used on the skin or topicals or who cannot use topical therapies. EBGLIS can be used with or without topical corticosteroids. Don't use if you are allergic to ebglis. Allergic reactions can occur that can be severe. Eye problems can occur. Tell your doctor if you have new or worsening eye problems. You should not receive a live vaccine when treated with eglis. Before starting ebglis. Tell your doctor if you have a parasitic infection. Infection.
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Ask your doctor about evglis and visit evglis.lilly.com or call 1-800-lilyrx or 1-800-545-5979 now.
- [07:34]
C
So right now, ACOG and AIUM and SMFM all agree the standard Definition of LGA is an estimated fetal weight of greater than the 90th percentile, with Macrosomia reserved for an absolute cutoff of 4,000 grams or more. So not all LGAs are macrosomic, but all macrosomics are LGA. Okay, not all LGAs are macrosomicSOMIC, but all macrosomics ARE LGA. So we've talked about that many times in the past. However. However. And I'm going to get to the data here in a minute. Having a large abdominal circumference that you note. Let's say it's 32 weeks and, oh, the abdomen is over 90 percentile, but the EFW is under. Don't ignore that either. So while you cannot diagnose lga, it shouldn't be ignored altogether because an isolated abdominal circumference, especially when measured between 28 and 34 weeks, is pretty darn sensitive. It's a strong predictor of pending LGA or macrosomia at birth. Okay, so I'm going to be very clear here. While AC greater than 90th percentile is not by itself diagnostic of LGA, it could signify greater growth down the line. In other words, you need to do a rate of growth ultrasound about three weeks later, or, you know, whatever is appropriate based on her EGA to track that fetal weight. Because based on who you read and Cochrane reviews also looked at this back in 2016, it has a positive likelihood ratio of anywhere from 5 up to 7 for predicting true LGA macrosomia at birth. All right, however, guys, here is. Don't lose this. Here is the rest of the story. Yes, it is true. It's not debated. The isolated abdominal circumference greater than the 90th percentile can be predictive as an isolated marker of fetal macrosomia at birth. In other words, impending fetal macrosomia. However, this is where you have to know statistics, because even though that likelihood ratio is high in these patients is like five or seven, it depends on, again, who you read. The issue is that still, nonetheless, and this is according to acog, its accuracy is not great. All right, so again, I don't want you to freak out that oh my goodness, my patient has a abdominal circumference greater than 90th percentile. That kid is doomed to be, you know, the weight of a small farm animal at birth. It's not, not necessarily. It's positive predictive value in the general population is still relatively poor. Okay, so that's the catch. Yes, there's a higher likelihood ratio, but still the positive predictive value for macrosomia still comes out to basically around 30 or 40%. It's not great. And that's on the high end. All right, so the positive predictive value is still way under the 50th percentile for sure. Where this lies in is that it has a very good negative predictive value. In other words, if the abdominal circumference is less than 90 percentile, the negative predictive value is like 96%. That that developing fetal macrosomia is not likely or in the cards for that child. All right, so again, this is where statistics come in. Yes, it is true. As a standalone sonographic factor, an isolated abdominal circumference greater than 90 can be a good predictor of macrosomia with a high likelihood ratio. However, nonetheless, the positive predictive value still is under 50%, with some saying it's about 30%. Same saying it's like 40%. And at the lowest end that I found is a positive predictive value of 24%. So it's an important thing to look at, but by itself. Here are the three take home messages. Number one, AC greater than 90th percentile is not diagnostic of anything. Number two, don't ignore it. Keep following it. And number three, let the patient relax, calm down, it's all right. Because while the likelihood ratio is there, it's positive predictive value when that is the only factor alone over 90th percentile is under 50th percent. Good point. To keep in mind that statistics matter. And that's why you got to know the difference between likelihood ratio, sensitivity, specificity, positive predictive value, and negative predictive value. So much better at ruling it out than it is at ruling it in. So there's two points to note here. And again, this is going to be a very quick episode. An AC of greater than 90% as a diagnosis is nothing. There is no diagnosis for that. It's just an AC of greater than 90th percent. What is the diagnosis? The diagnosis is it's a big fat abdomen, but there's nothing to do with that. However, you put a flag in your epic, you put a flag in your meditech, or whatever you use to say, huh? This is a risk factor. And you tell the patient, hey, everything looks great, but the abdomen of the child is over 90th percentile. That means that we need to check that again in three weeks, assuming that you're not yet delivered for X reasons, because that could imply that the baby is on the trajectory for being LGA macrosomic. Okay. And Remember, the cutoffs for macrosomia management is 5,000 grams without diabetes for offering of a C section and then 4,500 grams with diabetes for offering of a C section. Although some hospitals use 4250. You do whatever your hospital policy is, but as a national guidance, it's 4,500 with diabetes and greater than or at 5,000 grams without diabetes for the offering of a C section. Okay? So an abdominal circumference of greater than 90th percentile should not be ignored. I'll be very clear. Don't just go, huh, that's interesting. And be done with that. You definitely need to trend that again. It's a strong predictor of LGA and macrosomia at birth with some data. This was out of clinical ultrasounds in Medicine. They actually quoted it and said it is the single best predictor, end quote, when it's done between 28 and 34 weeks. So while it's not LGA at the moment, it's a risk factor for LGA down the road. Okay? And remember, it's just a risk factor. It does not mean that every fetus with an AC of greater than 9th percentile is going to absolutely hit macrosomia. It's just a likelihood ratio, if you want to call it an odds ratio, which they're similar but yet not interchangeable. It's just a likelihood ratio increase. Think about it like a hazard ratio or an odds ratio. It just raises the odds that the child will be a higher birth weight lga. So, and that's especially true, of course, if there is maternal hyperglycemia. So if mom is GBM and that baby's abdomen is 90% as an isolated finding before delivery, definitely get that EFW around 36 or 37 weeks. So you can plan management options, knowing, of course, that in general, you know, babies grow about 30 grams a day, so about 220 grams per week. So then you can figure out, you more or less predict what the baby will weigh from that last ultrasound. Okay, so anyway, very quick episode, because this was something that we discussed with our faculty team ourselves and with the residents. One of the residents asked, hey, if an isolated LGA is that diagnosis of lga? No, it's not. It's not a diagnosis of anything except a big abdomen. What is the diagnosis? The diagnosis of baby's kind of fat. But it doesn't mean anything unless the entire EFW is greater than 90%. And it is an indication to do a rate of growth ultrasound to make sure that the weight remains in an appropriate management scheme. So, Podcast family again, this was relatively quick, very targeted. A fetal abdominal circumference of greater than 90th percentile. What is a diagnosis? Nothing. It's not LGA. It is, however, a flag for impending LGA down the road, but not in and of itself is a diagnostic the entire EFW has to be greater than the 90th percentile, and to be macrosomic, it has to be greater than 4,000 grams or 4 kilos. Podcast family, as always, we're thankful for you. We're glad you're part of our podcast community. This was a quick one. Just reviewing what abdominal circumference over 90th percentile is. We'll see you on the next episode. This is Dr. Chapma's obgyn no spin podcast.