Episode 141 - Big babies Small Babies All Killer No Filler
[0:00] Welcome to the Great Birth Rebellion podcast. I'm your host,
[0:03] Dr. Melanie Jackson. I'm a clinical and research midwife with my PhD. And each episode, I cast a critical eye over current maternity care practice by grappling with research and historical knowledge to help you get the best out of your pregnancy, birth, and postpartum journey. So we'll look at the research on how the size of the baby, or they call it fetal size. I mean, I always call the babies babies, but how the size of the baby is determined. So what's a small baby? Small babies, they consider anything below 2.5 kilos. And when I was an early midwife, over 4.5 was considered to be a big baby. The research now is saying, well, a lot of things are saying 4 kilos is considered a big baby.
[0:53] The ACM guidelines and a lot of the research now is classifying babies over 4 kilos. As large for gestational age and certainly with all of the shoulder dystocia research and things for bigger babies in adverted commas they're looking at research from four kilos so in the ACM guidelines macrosomia is suspected so over four kilos it's a category c which means refer on I know so that's where we're up to that's where we're up to with large babies they're calling babies over four kilos, macrosomic and large for gestational age. So that's the terms. Those are the terms.
[1:34] 2.5, below 2.5 is small for gestational age. Over four is large for gestational age. And there's another classification, intrauterine growth restricted babies, so IUGR babies, which that's different. That's a small baby, but all of the proportions of its growth are out. So you can see things like big heads, but small bodies.
[1:58] So how do you determine the size of a baby? From a midwifery perspective, at first point of care, then we do what's called a symphysis pubis measurement or whatever they call it. Basically, it's a fundal height. You measure from the top of a woman's fundus, so the top of where you can feel her uterus, down to her pubic bones. And this is part of routine midwifery care. And I'm going to tell you a little bit about the accuracy of it because I do remember talking to a midwifery colleague who was like, is there any actual research around fundal height? Like, why do we do this? What's the research?
[2:36] So the research says that it can detect either a very small baby or a very large baby, but only 50% of the time is it accurate. So 50% of very big or very small babies are missed if you just use fundal height alone. That's the accuracy of it.
[2:59] But we as clinicians can increase the accuracy of this technique of measuring the baby from fundus to pubis. Because less experienced midwives have a higher level of inaccuracy. So when they looked at some of the research, it can get as low as 17% to 30% in inexperienced midwives. But with experienced midwives, they found it can get up to as accurate as 88% of the time, midwives accurately detecting a very large or a very small baby. So first, clinician's experience makes a difference to how effective this particular technique is. The other thing that adds to its accuracy is if the same clinician is doing it each time so if you have continuity of care and there's the same midwife measuring your fundal height every single time we can consider that measurement a more accurate measurement than if it was somebody different because everyone does it slightly differently and the idea of this technique of measurement is to get a record over time of how your baby's growing rather than a single event of measurement being kind of accurate to determine a big or small baby. It has to be done over time and plotted and fundal height very casually, very loosely correlates to gestation. So if I measure your fundus and you're 30 weeks pregnant and you're measuring 30.
[4:29] That seems to be a bit of a mid-range. The Australian College of Midwives guidelines suggest that three centimeters above or three centimeters below your gestation is still considered normal, a normal fundal height. So if you're 30 weeks pregnant and you're measuring 33, that's still within normal. And if you're 30 weeks pregnant and you're measuring 27, still considered a normal fundal height that doesn't trigger us to recommend any further assessment of the size of the baby.
[5:00] The fundal height can also be less accurate if the woman's carrying some extra weight, so bigger girls, or obviously if there's two babies in there, or the baby's not in a position that's up and down. So if it's transverse, so lying sideways, to increase the accuracy, if you standardize the technique for how to do fundal measurements. So the standard technique and the way we sort of should be doing it in adverted commas is you start the measurement from the top of the fundus and you bring it down to the pubic bone, and you do it with the tape measure facing down so you can't see the numbers. It's considered a more accurate way of doing it.
[5:43] And obviously the more you do it, the more experienced you get and then trying to keep your technique regular and similar and then for midwives to be offering continuity of care that's when a woman would get the most benefit out of a symphysis pubis measurement in terms of accuracy so basically the current research we've got on it is that there's actually not a lot of research on the accuracy of it but because it's an easy low-cost tool that can be applied by midwives in any setting really in most, depending on the country, but in most under-resourced or highly resourced countries,
[6:24] this is a really easy strategy. And it's been proven that when midwives are good at it and the model is effective, like continuity of care, it can be a useful clinical tool. It's also the expected professional standard. So actually, even if there wasn't any research as midwives, we would be expected to do a fundal height each time we see the woman. Yeah.
[6:50] That's all I have to say about fundal height. So that's one thing. What I have actually noticed is if you're having obstetric care where the obstetrician has access to an ultrasound in their rooms and that every time you go, they actually put an ultrasound on instead of putting their hands on you, that's not an evidence-based way. So regardless of access to ultrasound, your care provider should still be putting their hands on your belly to get a feeling for the size of the baby and the position and also measuring with a tape measure as the very first level of screening for the size of your baby. And I think fundal height too is something that everyone can understand. So if I said to my client who's 30 weeks, oh yeah, your fundal height is 30 centimeters, I've already explained to them like this is the normal range for things. They in their mind go, well, I'm 30 weeks, I'm measuring 30 centimeters, you know, this is one of the ways we can tell the size of baby. I'm feeling good about the size of my baby. Whereas not everybody, women can't look at their ultrasound and sort of go, oh yeah, I can see when you, if the obstetrician or whoever's doing the ultrasound says, oh, this is a big baby. That's only information that the clinician has access to. The woman doesn't have the information to be able to properly decipher whether or not that's a truthful interpretation of that ultrasound.
[8:20] Fundal height really can, is so accessible to women. If I had, did have a client who had a very, very high fundal height and, you know, and I said to her at 38 weeks, well, you know, your fundal height's 44. And she went, oh, okay, what are we going to do? What are we going to do now that we found that? She immediately understood what I understood. And so I feel like it's just a, like a way of actually giving women some knowledge and authority over what's going to happen rather than an ultrasound which holds back all the information to the clinician and isn't really accessible to the woman. So then if we move on from fundal height the next way that we can determine the size of babies is through ultrasound.
[9:06] So the research on this says that an ultrasound is accurate 70% of the time. So if you ultrasound 100 babies, 70 of those will receive what's considered an accurate weight estimation.
[9:22] The problem is, is that the acceptable accuracy of an ultrasound for weight and size is within 10%. So if you have an ultrasound and they say, okay, your baby is four kilos. The margin of error on that is 10% plus or minus 10%. So your baby who's on ultrasound is four kilos could be 4.4 kilos or could be 3.6 kilos. And that's considered an acceptable margin of error for a growth scan. So 70% of the time they can get the baby's weight within plus or minus 10 percent to them that's an acceptable margin of error they are saying we can estimate 70 percent of babies within 10 percent plus or minus that's considered accurate and so what they'll if someone says to you yes they're accurate 70 percent of the time they are accurate 70 percent of the time but their definition of accuracy is plus or minus 10 percent so you know if you're happy with that level of accuracy i wouldn't i'm not happy with it And spoiler alert, the research says that's not a good enough level of accuracy to be using ultrasound as a clinical decision-making tool. So two-thirds of the time, they can accurately diagnose the size of your baby, but within plus or minus 10%. And the other 30% of the time, so 20%.
[10:46] Only two in three babies can be accurately sized, accurately. So the research is not in favour because of these, the inaccuracies. The research is not in favour of routine growth scans for women who are at low risk of a very small or a very large baby. So when they, they've actually looked at this and routinely giving everyone a third trimester ultrasound didn't improve outcomes at all. But it does increase intervention as a result of what they find. So they applied an inaccurate ultrasound to all women, then they started acting on these inaccurate results. So, wow, your baby is too small, we should induce you to get it out, or your baby is too big, so we should induce you to get it out. So these growth scans increased intervention, but didn't improve any outcomes. The research on it suggests that it's actually a wasteful use of a resource. It's not cost effective. And to expect every single pregnant woman to somehow be able to access an ultrasound at 36 weeks is considered an unreasonable level of maternity care, considering it hasn't actually demonstrated itself to improve any sort of outcomes.
[12:04] We really should be saving this technology for women who actually need it and who actually might benefit rather than just doling out ultrasounds to every single woman and multiple ultrasounds of pregnancy.
[12:17] Women who actually need ultrasounds have trouble getting in on time, probably because we're overusing this tool to women who don't actually need it. And it's not even accurate. it. And so all of these stats that I'm giving you, this is all based on actual research papers, which if you're on the mailing list, you'll get access to in the resource folder. So don't just take my word for it. Feel free to read all this. All these stats are just plucked from actual papers. Yeah. So basically what we know is we cannot, there's actually no way that your clinician can accurately tell you if you have a very large or a very small baby. So below 2.5 or above 4 kilos, until your baby's out. So if you've gotten the word from your care provider that your baby's so big it's not going to come out, so maybe we should do a cesarean section, or your baby's so big we're worried about its growth that we want to bring it out early, just know that no one, doesn't matter how good they are, can accurately determine the exact size of your baby.
[13:21] Something that ultrasound can potentially help with is if your baby is, if they say your baby is small for gestational age, that's one thing. That means all of the parts are small sort of equally. But if it's intrauterine growth restricted, which we're going to talk about the reasons why your baby could be small like this, the ultrasound results are still not accurate for weight, but they can give you measurements of the baby's head versus the baby's tummy versus the baby's leg length and all these things so if your baby's head is on the 50th centile but the rest of the baby's body is on the 10th centile all the other way around if there's some big major discrepancies you might be looking at a growth restricted baby rather than just a small baby and growth restriction is pathological so ultrasound might be helpful in that regard but But in terms of the actual weight, if the baby is growth restricted, the weight still doesn't matter because it's about the proportions of the baby. So we can't completely throw it out. But the thought is, is that we shouldn't be making clinical decisions based on a single sort of growth scan, for example, doing a growth scan and saying your baby's big, we're going to induce you, or your baby's small, we're going to induce you. It's not considered appropriate clinical decision making.
[14:46] And so there's there can be completely normal reasons for why your baby might be small or big so even if someone says right you've got a small baby or you've got a big baby let's look at the reasons why that actually might be completely normal and fine for you firstly people of different ethnicities make different sized babies so the standards are catered to a white western demographic most of the time unless you're looking at research and there are research papers that seek to create growth charts for all different ethnicities and that's what we need to be working towards is individualized unique growth expectations and size expectations for all different types of.
[15:37] Ethnicities. So it's really a fundamentally racist idea that everyone's baby should conform to a Western standard of normal. And if the babies don't fit this white Western idea of normal, then there's something wrong that needs fixing. And I know some people look at this and say, oh gosh, Mel, that's not racist, but.
[15:59] You know, so if you deem something wrong because it doesn't conform to a dominant Western idea, then that disadvantages and it belittles what's true for people of other ethnicities and it demonstrates that racism. And it's actually built into the maternity care system. Like individual clinicians might not be personally racist, but by assuming that the white Western standard of baby size is correct, we are subconsciously upholding a racist approach. We can't just apply this blanket like your baby's too small and your baby's too big because some ethnicities and some people will naturally make smaller babies. Some will naturally make bigger babies, but we can't pathologize that against a Western standard. But that's the other reason why you might make a smaller or larger baby is just genetics.
[16:53] Maybe your mom did, or maybe your sisters did, and you're just a healthy woman with a bigger or a smaller baby on board. And some places call these, so there's a word, they're just constitutionally
[17:03] small or constitutionally large infants. Difference there's a difference between small for gestational age necessarily and just constitutionally small so that but you can't work all this out until they're out so those are sort of two reasons why it could just be normal because you're just a normal well healthy baby healthy woman and your baby's just was supposed to be smaller but there are.
[17:29] Abnormal or pathological reasons for why a baby. So we'll start with why a baby might be small. If you smoke or use drugs or particular medications, having these, we know that these babies are smaller. Particularly smoking during pregnancy periodically restricts blood flow through the placenta and so essentially kind of malnourishes the baby in small increments over it's gestation. And so they are statistically smaller babies for women who are smoking or using drugs or some particular medications that might have a similar effect. Passive smoking can also have a similar impact, which is why as clinicians, we do ask women about passive smoking. And interestingly, there is actually research on how smoke or nicotine or passive smoking impacts different ethnicities.
[18:22] So black women seem to have a bigger impact upon their pregnancies if they've been exposed to secondhand smoke compared to white women. So they've done this with a few different ethnicities in a few different locations and found that there can be the way that different bodies retain the products that you would inhale with passive smoking is different across races and cultures just because of our genetic makeup. I'm sure it's compounded, but the particular, I kind of stumbled across this research where it's like there's all these nuances of how we're genetically made up, of how we respond to certain environmental things. And so, yeah, that was just something that I kind of went, oh, that's interesting. But it can affect people differently.
[19:13] So the issue is, is that we haven't really diversified research. We've focused too like smally on, that's not a word, shallowly. And some research tries, like when you're doing a research project, you will ask people their ethnicity and all that kind of thing. The problem is, is that then when research is applied in a clinical setting, they don't have five different guidelines. If you have, if you've identified that the demographic of your service, maternity service area includes a high number of Iranian women and Indian women and Japanese women and Tongan women, for example, there's not four separate guidelines depending on. So even if the research is there, it's not being applied in a logical way. That's the issue with systematic maternity care is that there's one system and it's just supposed to be a blanket, one size fits all, but it's not true because we're all different. So that's one reason why you could have a small baby for a pathological reason.
[20:15] The other one that's kind of newish, like I feel like in the last few years, is the increased use of nuchal translucency ultrasounds as a more routine test done between about 12 and 14 weeks. And it was traditionally marketed as a way of determining Down syndrome risk or genetic screening. They give you a risk, you know, ratio. But with this blood, they also do a blood test and they can give you a reading on what's called a pap A level.
[20:47] And it's a placental hormone. So if you have a low pap A, so below 0.4, they've discovered that a low pap A puts women at more risk of having growth-restricted babies, smaller babies. They're at higher risk of preterm birth and also preeclampsia so there's something in that and sometimes they recommend that women particularly they've had repeat multiple miscarriages or preterm births before or history of low birth weight babies if they identify a low pap a on the nuchal translucency ultrasound they will sometimes recommend routine use like daily use of aspirin through your pregnancy, and that's thought to increase blood flow through the placenta. So this pap A somehow, and I'm not across it complete, like the physiology completely, but it can impact on the efficiency of blood flow through the placenta if the pap A levels are low because it speaks to the quality of the placentation, like the implantation of the placenta. If you've got low pap A, and a history that you can draw on that kind of indicates that for some reason this is happening for you, that could be a pathological reason. So worth looking into.
[22:09] And the other thing with low PAP-A is because it's considered a risk factor, then they recommend these serial routine growth scans, right? So the women are on, they got a low PAP-A, so they're at risk. So then they're on aspirin, which also, you know, you're on a medicine for the whole birth then, for the whole pregnancy then and then you're going in for these routine growth scans um and so there's kind of just this heightened level of attention that and you know the minute they see something that's slightly untoward they're like well see see it's an issue we're gonna do this we're gonna do that and and I think it's more of an issue now because of the increased popularity of the nuchal translucency when when I first started midwifery it was kind of only women who were kind of considered at risk of genetic issues with their baby so older women or women with a history or IVF pregnancies and things like that were actually encouraged to do the nuchal translucency screening and other women who were young healthy with with no particular risk factors were kind of confidently not getting those ultrasounds now we've got more women having information about their pap a levels and so then there's more action and more interest in what do we do now, and I've had clients, you know, who've gotten the nuchal translucency and then have decided one of them went on aspirin and so then declined the growth scans.
[23:39] The other one decided not to go on aspirin and accept all the growth scans because she chose not to go on aspirin. So, you know, it's not necessarily right or wrong to get the papay. I guess it gives you some information about your possible risk factors and then you can make decisions about how you want to act. Okay, so the next abnormal or pathological reason why your baby might be small is if you have high blood pressure through your pregnancy or preeclampsia or what we call HELP syndrome. So again, these can be, the root of them can be placental, which explains why the babies are at more risk of being small and then they manifest as high blood pressure, preeclampsia and HELP syndromia. Placental insufficiency is another one, but again, that's usually a result of one of those conditions we just spoke about. It might not be in itself the things that started it. It might be a symptom of what's going on, but anything that reduces blood flow and activity of the placenta is going to impact the size and development of your baby. So if the baby has a health condition, a developmental abnormality or a congenital abnormality that can impact their growth. So again, ultrasounds could tell you some of this. And some babies are born with syndromes, genetic syndromes that take time to diagnose that we can't maybe not actually have a screening test for, some more rare things.
[25:04] The other thing that can give you a small baby is a maternal infection such as syphilis, toxoplasmosis, CMV, so cytomegalovirus. So if a baby's born very small, we can do what's called a torch assay, I think it's called, or a torch test on the baby, which tests multiple viruses that can impact on the growth of a baby because of a maternal infection, because the mum got an infection during pregnancy.
[25:32] And the other thing that can give you a small baby for a bad reason is maternal malnutrition or calorie restriction and starvation. So literally, women who have eating disorders during pregnancy or that are calorie restricting in order to maintain an unrealistic weight level, or obviously in less resource countries, women who actually don't have enough
[25:57] food during their pregnancy impacts upon the size of your baby. So what we might do now is talk about what kind of interventions are offered to women who are diagnosed with smaller babies. So, okay, so say, let's go hypothetical, you presented to your care provider your 36 weeks and they say, mate, your baby is really small.
[26:21] And we need to induce you to get the baby out. This is what they do. It seems weird. People go, so my baby's really small, so you want to get it out of me. This doesn't make a lot of sense. What they're saying when they say your baby's small, we want to get it out of you. They think that something in your body is a danger to your baby and that they can do a better job or you can do a better job on looking after that baby when it's out instead of in. Part of it is that care providers are not very good at dealing with uncertainty. And so if your baby's out, there's a lot more certainty. They can see it. They can measure stuff. They can see how much food's going in and what's coming out. So part of it is wanting an increased level of certainty about what's going on. They're not comfortable with not knowing if or why your baby is small. And so they want to resolve it by getting it out. The issue with that is that if you bring a constitutionally small baby out unnecessarily through the process of usually induction, then you're doing that baby a massive disservice because it's already little and it needed more time in its mama to get to a full-term mature size. Then we start to have issues of prematurity. So we increase the burden on the healthcare system by bringing these well, constitutionally well babies out early and we know that you can't accurately diagnose.
[27:48] A very, very small baby by ultrasound or even really by fundal height properly. That begs the question of like, should we be bringing small babies out versus what they want to do is they want to bring the intrauterine growth restricted babies out. That's what they're aiming for. The aim of bringing out a small baby is, is it intrauterine growth restricted because there's something wrong on the inside? And if we can disconnect the baby from its mother, then possibly we can reduce the impact of whatever's going on in the mom's body, the impact on the baby. So that's the rationale. And there are some generally IUGR, intrauterine growth restricted babies, and maybe they would do better on the outside. But the problem is, is that we can't accurately diagnose the size of a baby until it's out already. And then in hindsight, we could say, well, we're glad we got that one out or, ooh, that one was actually fine and we've used ultrasound as a tool to make a very big decision of inducing a baby that didn't need to be induced.
[29:00] And so you've got to be asking questions of your care provider of, is my baby intrauterine growth restricted? Is that what you're worried about? In which case, we can do things like check placental blood flow. You can check your levels of PAPA if you had a nuchal translucency. You can do all this other screening to work out, okay, why is my baby abnormally or pathologically small? Do I have a risk factor for this? And therefore, is there a good reason to start acting and changing the gestation of when this baby is going to be born?
[29:33] Or have you always grown small babies? Has your mom grown small babies? What ethnicity are you? What's your diet like? I think it's important if you know as a woman, no, I feel incredibly healthy. I know what I'm eating. I feel that my baby's well and that it's a normal size for me. That's important information because women do have internal information about how well their baby is. Yeah. Yeah, and so that's what we've got to say today about small for gestational age babies and determining size, and there'll be lots of beautiful papers in
[30:08] the resource folder about that. So we're going to dive straight into the big babies chat. All right, so abnormal reasons. So we already worked out normal reasons why your baby might be big is your ethnicity and your genetics. It's just supposed to be that way, and your body can do it, and you're well and healthy, and don't worry about it because that's the size that your body's going to grow your baby because it knows it can get it out because that's what you were made for. So that's the main reason why you'll have a big baby is because it was supposed to be big. There are abnormal reasons for why your baby might be big. And the issue is not that it's big, it's that it's bigger than it's supposed to be for your body.
[30:50] Because typically what we feel as midwives is that you will grow the size baby that you can get out because there's a communication between your baby and your body and they each know what size they are and what size they need to be in order to make this relationship of baby coming out of your body work. But there are sometimes states of pathology that will change how our body functions. And so then it can mess with that physiology. The main reason why people worry for big babies is the concern about gestational diabetes. And, you know, obviously gestational diabetes diagnosis is fraught with controversy. And you can listen to our gestational diabetes screening episode to get an understanding of that. But if you have true diabetes, like definitely gestational diabetic, and it's uncontrolled or undiagnosed.
[31:48] Then your baby is at risk of growing bigger than it should have. And they grow disproportionately larger shoulders. It's not like they get big everywhere. There's a typical sort of weight pattern that gestational diabetic babies have that makes their shoulders bigger than they should be. This is only for true uncontrolled or undiagnosed diabetes. For women who are listening, who've been diagnosed with gestational diabetes, you're doing your sugars every day. You're checking in with whoever's checking up on you and all your blood sugars have been normal. You have what's called controlled diabetes and you don't have a risk of an abnormally large baby because your risk factor of gestational diabetes has been controlled. And so for all intents and purposes, you're not at risk of a big baby. So if you're being encouraged to be induced because you have diabetes at 38 weeks, but for your whole pregnancy, you can demonstrate that your blood sugar levels have remained within the normal range, then you don't have clinically manifested gestational diabetes. You've got controlled diabetes and you've got a well healthy pregnancy and a baby that's not at risk of getting too big.
[33:09] All right so the next reason why your baby the abnormal reason for why your baby might be big and this is for women who've got poor eating habits and have gained a lot of weight in pregnancy. They will typically also grow bigger babies because if you're eating a lot of junk food and gaining weight as a result. I'm just saying for women who are eating poorly, high-sugar diets, high-carb diets and not looking after themselves in pregnancy and as a result are gaining excessive amounts of weight, this is evidence-based and I'm not going to fat shame. That's not what I'm here for. But I'm just saying if that's been your pattern is to not nourish yourself well and have a high-sugar diet.
[33:55] Like, can we acknowledge that there are some times that women need to make decisions for their health to reduce their risk factors? Like, I just go for the jugular on all of these hard topics. I'm like, here's the facts. And look, the research is that women who gain a lot of weight, and I'm talking like, you know, 30 or 40 kilos in their pregnancy, typically will grow a larger baby as well. Some, there is weight gain that occurs to us in pregnancy that we have absolutely no control over. So I'm not talking about that. I'm not talking about just because you gain weight because you're pregnant. So, but, you know, that's what the research shows. The women, you know, it's, you can grow an abnormally large baby because it's also gained an abnormal amount of weight in line with what's happened to you through your pregnancy.
[34:44] And then obviously the really kind of obvious one is that pregnancies that go beyond 42 weeks that are post-term. So the longer you are pregnant, the bigger your baby's going to be. It's not necessarily an abnormal thing to go to 42 weeks, but past 42 weeks is considered abnormal. So if you're past 42 weeks, that's an abnormal reason for why you have a big baby and consider that, you know, that puts it into a risk category.
[35:13] So those are the three abnormal reasons. All right. So why do we worry about big babies? Why is everyone actually obsessed with trying to work out the size of your baby? And then if it's big, wanting to get it out? Because that's the reality is that if you're diagnosed with a baby that's over four kilos at term or, you know, for its gestation, then your care provider may recommend an induction to get the baby out early or even more severe is they might tell you your baby's so big that they don't believe it's going to come out and they might want to take you just for an immediate cesarean and not even offer the option of an induction. So that's why it's important to start working out is my baby big but we already heard that we can't accurately diagnose the size of baby until it's born because fundal height measurement and ultrasound measurement aren't accurate enough to give you enough clinical information to make a decision on what to do because they're not, it doesn't give you good enough information.
[36:20] We'll talk about the first thing and that is shoulder dystocia. So they'll say the bigger baby is, the more risk it is at shoulder dystocia. And I've looked at so many shoulder dystocia papers to try and actually disprove this statement. That's given to women of, like, the bigger your baby gets, the more chance you have of shoulder dyslexia. You know, and I'm like, no way, women's pelvises can do it, babies can come out, doesn't matter their size.
[36:51] And unfortunately... I'm here to tell you that bigger babies do have a significantly increased risk of having shoulder dystocia the bigger they get past four kilos. So if you have a baby between 2.5 and four kilos, and here's where I think the classification changed from 4.5 kilos as a big baby to four kilos.
[37:17] 0.6% to 1.4% of babies between 2.5 and four kilos will experience a shoulder dystocia. So pretty rare. For babies who are over four kilos, the stat goes up to five to nine percent of babies over four kilos will experience a shoulder dystocia and it's exponential. So the bigger the baby gets, the more likely it is to happen.
[37:44] I feel like this is some Cochrane reviews. This is compiled data. So this is like, it's pretty damning research. I kept pushing this episode off because I kept looking for research. I'm like, please tell me it isn't so. So what the Cochrane Review did, and this is a 2023 paper, so it's probably the most up-to-date one we've got, and it's called Induction of Labor at or Near Term for Suspected Macrosomia. Now it it showed that if you induced women who had suspected macrosomia suspected large babies their babies are approximately 200 grams lighter which no which is no brainer because they're bringing them out early the rates of shoulder dystocia were less in the induction group than they were in the group that was just observed and so I don't know what events were around the physiological birth of bigger suspected bigger babies because these were not all definitely bigger but what they did see was a reduction in shoulder dystocia with early induction for babies who are suspected of being big but they did not recommend routine induction for babies who are suspected as macrosomic, even though they found those stats, even though, yes.
[39:12] Inducing women early who suspected they have large babies does reduce shoulder dystocia, it increases the risk for a whole lot of other stuff, right? So the argument is, is we can't accurately diagnose macrosomic babies. And so therefore, we shouldn't be routinely inducing them. However, if you do choose an induction, statistically, you are at reduced risk of shoulder dystocia, but you increase your risk of other things like PPH and prematurity and an unnecessary induction. So don't use this as a reason to just induce women because this is still controversial. We still don't have good enough information to accurately diagnose size in order to confidently use induction as a strategy for macrosomic babies because we're not good enough at diagnosing macrosomic babies yet to be confidently inducing them. So it was a double-edged, it sort of just tells people you're at a bit more risk. You know, shoulder dystocia, we're good at managing shoulder dystocia. We're good at also creating shoulder dystocias, putting women on the bed and doing manoeuvres.
[40:30] Even vacuum extraction and forceps puts babies at increased risk of all these things. So there are things that will increase your risk of shoulder dystocia. I guess what I'm trying to say is that a bigger baby does have an increased risk of shoulder dystocia. And if you induce that bigger baby earlier that reduces its risk because it reduces its size. We would definitely need an entire episode to talk about shoulder dystocia but I what I guess the point of this discussion has been is that the reason why everyone's panicking about big babies is that they're frightened that your baby's going to have a shoulder dystocia and so they want to avoid it by bringing your baby out before it gets too big but they can't even really diagnose how big your baby is and that's where the issue lies is that, okay, maybe if we could accurately diagnose larger babies, maybe an induction could save people.
[41:25] A large percentage of babies from getting stuck. But obviously, we're reducing that risk, but we're adding a whole lot of others. And that's the issue. I think that's what Cochrane is saying is, how do we justify reducing the risk of shoulder dystocia by using induction when we know that induction carries a whole other collection of risks? So you're just moving the risk to another spot. So although maybe the induction meant they didn't have a shoulder dystocia but then we also actually created a whole lot of other issues and introduced a whole lot of other risk. When we're sort of talking about if you've got a bigger a suspected bigger baby on board and we know that definitely bigger babies have got a higher risk of shoulder dystocia the woman then gets to decide which risk she's willing to accept.
[42:16] What we also know is that if you've had a shoulder dystocia at a previous birth you are at an increased risk of having a shoulder associate another birth. And so some women who maybe have experienced a catastrophic and very traumatic shoulder to social might say, well, I like that information. That information means that if I have a suspected large baby... I would want to choose an induction knowing that it will reduce my risk of shoulder dystocia and I accept the possibility that other risks could eventuate, but I'm more frightened of the risk of shoulder dystocia. So although we don't like the
[42:53] findings because it's in favour of an induction, it's just information. I'm not telling women what they should do. If a woman wants to choose that, at least we have some information about what the options are. So that's what I was going to say about that. And this Cochrane paper will be in the resources so everyone can have a read of it. We shouldn't be looking. So the research says we shouldn't be looking at low-risk women for gross scans.
[43:21] But, for example, if you have a client who's got uncontrolled diabetes or one of the other risk factors, and you're looking and their fundal height is suddenly five centimeters higher than their gestation or you're feeling the baby under your hands and you're thinking, well, this is a big baby. Are we currently experiencing a big baby for abnormal reasons, in which case intervention might actually improve the outcomes? What we're seeing is the application of screening across the board for low-risk women and then using that to diagnose macrosomia and then using macrosomia as an excuse to do early inductions. That's where the problem is, is we're pathologizing normally large babies. And then the next reason why people get all panicky around big babies is there's this other thing called um cephalopelvic disproportion so cpd so c cpd cephalopelvic disproportion is when you know and we've all heard someone be told this well women are being told that your baby's so big that it won't fit out your pelvis and therefore we're not even going to attempt an induction we're just going to give you a cesarean section so this is the worst of it really because it take it's.
[44:39] A complete disbelief that the baby's even going to fit through the woman's pelvis. And so women get worried. They're like, oh my gosh, the doctor said, or someone said, I'm not going to say the doctor, but someone said this baby couldn't fit and therefore I needed a cesarean section. Okay. We cannot in any way measure the pelvic inlet of a woman to determine if the size of that baby's head is going to be able to get out. There's no way of determining that while you're pregnant. This is something that you're worried about, like, oh, maybe the head's not going to fit through. So guess what happens? If you're in the very rare situation where your baby's head is too big for your pelvis, the only thing that's going to happen is it's not going to come out in labor. And you're going to labor and it won't progress normally and it'll be slow and it might be extra painful because your body's working super hard to try and get the baby out. The baby might get into a level of distress or you just won't continue to progress and in hindsight or during labor you can actually diagnose the possibility that you're experiencing cephalopelvic disproportion and if that's genuinely what is happening then thank goodness for cesarean sections because your baby wasn't going to come out. It's super rare. I'm really only convinced that I've seen it twice in 14 years as a private midwife.
[46:09] So with true keflopelvic disproportion, the baby won't come out because it truly is too big to fit through your pelvis. There's a few reasons for why that might be. You might have had a pelvic injury. You might have a pelvic deformity. You might have issues with the pelvic shape because of malnutrition. And this can be reasons of, you know, in less developed countries. So there are reasons for why a baby might not be able to get through the pelvis and it might not be the size of the baby it might be the shape or makeup of the woman's pelvis and so if that's the case we've got the beautiful intervention of cesarean section that is really readily accessible and it's it's not a profoundly dangerous situation in a western environment because we're so heavily monitor labor and birth that we can pretty quickly pick up if you're experiencing CPD. The baby shows clear signs. There's clear signs in the labor and we sort of go, oh, probably that baby's not going to come out. And then they reach a level of distress where they sort of go, oh, we've got to get the baby out now. And so you can, in hindsight, sort of go, we think that maybe this was kephalopelvic disproportion and that's why your baby didn't come down. That's why your baby sat high and didn't send into the pelvis. So.
[47:31] But we can't, there's no way of determining if the baby's head is not going to fit through your pelvis before you actually try.
[47:38] There's no harm if somebody says your baby's too big to get through your pelvis, there's no harm in saying, well, that might be so, but I'd like to try. And if it doesn't work, then I will accept a cesarean section. But a cold cesarean section, just because your care provider thinks that your baby's too big to fit through your pelvis is poor clinical practice on the part of the clinician. So I think take home messages around big babies or suspected big babies is that firstly, we as clinicians, even in Western countries, don't have effective tools to accurately measure the size of your baby. We can measure it within 10% of its potential size, only 70% of the time. So two-thirds of the time, we can tell you where roughly your baby sits on the scale of big baby to small baby. If you've been told your baby's four kilos, there's a 10% plus or minus difference in that. So your baby could be 4.4 kilos or it could be 3.6 kilos. And that's if you're in the 70% of women who have been accurately diagnosed or that the baby's size has been accurately reported on. There's 30% of ultrasounds that will inaccurately report on the size of your baby. And so there's more than a 10% discrepancy. So we know that we can't properly...
[49:04] Determine the size of a baby. We also know that the research does not and the guidelines don't favor inducing women early because we suspect their baby's big. Not any of the Australian guidelines. The NICE guidelines also don't recommend it in the UK. The Cochrane Database of Systematic Reviews, although they found some benefit to inducing women early in terms of shoulder dystocia outcomes still did not recommend routine induction for babies who are suspected of being large because we don't actually have the diagnostic tools to confirm that babies are macrosomic.
[49:44] There's a difference between shoulder dystocia and a poor outcome. So although we're talking about increased risk of shoulder dystocia, most can be very easily resolved without injury to the baby. I think that's the crux of why we're doing this episode is that the amount of intervention that women are exposed to because we think their babies are big is disproportionate to the risk that is posed to them because we don't have very good technology to determine big babies and so we're acting as if we do and doing all these things to women and then only one percent of women have babies that are over 4.5 kilos but we've given all this intervention through fear because we've been using poor screening techniques that don't actually work accurately.
[50:37] We've got to remember that the thing that your care provider might be scared of doesn't necessarily have to be the thing that you're scared of. So even though they might want to induce you because they're frightened of shoulder dystocia, you might be more frightened of induction than you are of shoulder dystocia. And so that means that your choice will be different. You might choose to accept the risk that maybe your baby's big and that maybe your baby might be at risk of shoulder dystocia. But maybe a shoulder dystocia is not worse in your mind than an induction or a cesarean section. And so I think it's about, you know, risk is always about, it's a perception, it's not fact.
[51:19] So it's all about what you perceive is the most risky thing. So I think risk is not absolute. It's a perception.
[51:27] And the other thing I want to say about that in response to like, what can you do if you've been told that your baby's big? Firstly, I think women should feel confident to ask like, what's your hospital routine around growth scans in the third trimester? Are they routinely done? and why are you giving me one if I'm at low risk of a big or very small baby? And so if they don't have a very good reason for why they're intervening or monitoring your pregnancy, then consider maybe, tapping out of this whole issue by not accepting the growth scan that we know is inaccurate. I've had clients who have only wanted an ultrasound to find out one thing and we've very specifically written on the feral, only determine placental position, do not measure or check the baby. And that was a specific request of the women and you can do that. And so I think checking what the hospital policies are, wherever you're going to give birth, and then also discovering what the policy is.
[52:35] So let's say you do want to have that third trimester ultrasound and they report the size of your baby. What's the policy on that? Would you be inducing and all that kind of stuff? So understanding what your hospital or care provider would normally do in those situations and assessing your own level of risk. So if you go, well, I'm not at risk of a very large or a very small baby, therefore, I should not even be having this third trimester scan to check specifically for size. So, yeah, I think that would be my take home point is that you could completely tap out of the smaller gestational age and larger gestational age discussion by declining a routine growth scan in your third trimester.
[53:18] It was a big episode. what I feel that you can take away from this is that we're yet to start recommending routine inductions for large babies because we can't accurately diagnose large babies. So if a care provider is recommending induction and you have no existing risk factors for having an abnormally large baby, for example, if you've got uncontrolled diabetes or one of the other risk factors that we spoke about earlier, then the research is on the side of not changing anything in your care and not actually encouraging cesarean section or induction of labor for suspected large or macrosomic babies. If you want any of the information, research papers that we spoke about in this episode, then you can get on the mailing list for this podcast. Once you get on the mailing list, you'll be sent a link to the resource folders for this podcast, and that includes folders for every single episode and all the research papers that we use. To get access to the resources for each podcast episode, join the mailing list at melaniethemidwife.com. And to support the work of this podcast, wear the rebellion in the form of clothing and other merch at thegreatbirthrebellion.com.
This transcript was produced by ai technology and may contain errors.
©2025 Melanie The Midwife
