Episode 98 - Gestational diabetes screening
[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. Today we are specifically talking about the diagnosis of gestational diabetes. Next episode, I've invited Lily Nichols to come and speak about the management of gestational diabetes. She wrote the incredible book, Real Food for Gestational Diabetes, and she's coming on in our next episode. So I wanted to bundle this episode in with hers. This episode is specifically about screening for gestational diabetes and the techniques that we use to try and diagnose gestational diabetes and of course
[0:56] all the issues that arise with that kind of a practice. So this is a re-edit of episode 18 so that if you're coming to this podcast with the specific interest of learning about gestational diabetes the topics will be smack bang together. So let's get into it.
[1:14] Now, gestational diabetes is a special kind of diabetes that only happens for pregnant women. You can't get gestational diabetes unless you're gestating. So this is not pre-existing diabetes. Like if you've got diabetes and then you become pregnant, you don't then have gestational diabetes. And this is not type 1 diabetes where you're sometimes born with it or it develops and you need insulin. This is specifically diabetes that occurs for women who didn't previously have diabetes but then became diabetic during their pregnancy. And there's a whole reason behind why that might happen. And we will talk about it in another episode when we talk about diabetes. But essentially, the placenta changes how your body can use glucose that's in your bloodstream. And so sometimes that can tip women into a diabetic state. Once you stop being pregnant and your placenta is born, you are effectively cured of gestational diabetes and you may be at risk of developing diabetes later down the track but at that point the treatment for gestational diabetes
[2:14] is firstly to manage it in pregnancy but then once the baby's out you're effectively cured. So then what do we do? Let's talk about how it's screened for for pregnant women. So there's two camps, there's what we call universal screening for gestational diabetes.
[2:30] And then there's risk-based screening for gestational diabetes. And it's typically done, I'm going to talk very broad terms, because speaking generally, what most women will be exposed to will be universal screening. What that means is there's a bit of a blanket rule in most hospitals that everybody gets screened for gestational diabetes, usually between 24 and 28 weeks, if you are not deemed to be at risk. Sometimes if you're deemed to be at risk, they'll recommend glucose tolerance testing earlier in your pregnancy. And with universal screening, they just screen everybody. But with risk-based screening, they sit down and go, right, do you have any particular risk that will make you more prone to developing gestational diabetes than another woman? For women who are considered overweight, if you've had a previous baby that's bigger than 4.5 kilos, if you previously had gestational diabetes, if you've got a first degree relative with diabetes, like a sibling or your mom or your dad, you're also considered to have potentially genetic predisposition to it. The other thing that's flagged now is age. So as women are having their babies older, everybody's concerned that the older you get, the sicker you'll be in your pregnancies. I'm not saying that's the truth. I'm just saying that's what the hospital system sees. And yeah, ethnicity is another one. I think there are some people, groups who seem to be more sensitive to developing gestational diabetes.
[3:56] And the other reason why you might be deemed to be at risk is if you're carrying multiple babies, twins or triplets. There's more placental sites, so potentially more opportunity to develop gestational diabetes.
[4:08] So you might be in a setting that does universal testing. So basically it doesn't matter if you have any risk factors or anything, whether you're young and healthy or old and sick, whatever, there's multiple
[4:21] categories in between there, but everybody gets a screen for gestational diabetes. In a risk-based model, only the women who are considered to have risk factors for gestational diabetes will be screened and the other ones will just go about their pregnancy having skipped that screening. So probably if you're pregnant and you're going through mainstream maternity services, you're most likely between 24 and 28 weeks be offered this formal glucose tolerance test. It's the diagnostic test for gestational diabetes. So if this test comes back and the range of blood sugar is above their considered range and we'll talk about the issues of what the cutoff numbers are as to whether or not you have diabetes. It comes back high, you're considered to have diabetes after having done that test. But basically what we're saying is if you're pregnant, be prepared that at some point, usually between 24 and 28 weeks, you'll be asked by your care provider to do or if you want to do the formal glucose tolerance test. Sometimes it's called the FGTT or the glucose tolerance test GTT. And this is how it's done is you would arrive to usually a pathology lab or to the hospital.
[5:30] For your routine antenatal care and they would test your blood sugar on arrival through a blood test then they give you a drink which has 75 grams sugar it's got obviously other ingredients but that's the the idea is that everybody gets 75 grams of sugar and then one hour after having that they take your blood test again and then two hours after they take it again so the idea of this is they're trying to see how your body is digesting, processing, and eliminating or using sugar during your pregnancy. And you're in a state of diabetes if your body's having trouble using that sugar that you've just had. So if you had diabetes, theoretically, that one hour and two hour reading would be high. So one thing they do to decide if you have diabetes or not is there's a cutoff limit as if at one hour if your blood sugar is over a particular level they'd say that's considered a diagnosis for diabetes and again at two hours if it's over a certain limit then you would be diagnosed with gestational diabetes because your body's demonstrated that it's having trouble processing the sugar that's given to it and therefore it's
[6:46] assumed that you're diabetic.
[6:47] Now there's a bit of contention and I'm again not going to go into detail about it, but the cutoffs for what's diagnosed as diabetic or not are controversial to say the least. And so we're still really haven't decided what cutoff is diagnostic for diabetes or not. And recently they changed the cutoffs to lower the levels. And so there's a lot more women being diagnosed with gestational diabetes. And although this is the Great Birth Rebellion, I want to seriously plug another podcast in this moment because they did an amazing episode. I think there might have even been two episodes on gestational diabetes. If you haven't found it yet, the Midwives Cauldron has done an insanely good quality episode on gestational diabetes. So listen to that because it's the prequel to this one, I feel. I'm not repeating what they've said. So what I'm saying is it's contentious and that the expectation on pregnant women is to keep their blood sugar lower than non-pregnant people. So there's a Cochrane Review. I'm basically trying to get to the Cochrane Review 2017, which has told us basically that we have absolutely zero quality evidence that tells us what the best way to screen for gestational diabetes is. Regardless of what the cutoffs are, there's no evidence for any of it. There's actually nothing. Like we're doing all of this on a wild assumption. So according to Douglas Hayley Moyer and Barrett Smith Pathology Labs.
[8:15] They're saying anything greater than 5.1 for the initial fasting glucose, one hour anything greater than 10, or two hours anything greater than 8.5. So if we vaguely have a look at what cutoffs we're using to diagnose gestational diabetes in pregnancy.
[8:34] The contention is that it used to be one classification, but they've recently changed it, and different facilities and different healthcare providers are divided on which classification or which diagnostic cutoffs diagnose diabetes. But when I do, if I do gestational diabetes testing for my clients, when I get the report back, underneath it, it tells me what kind of criteria they've used to diagnose gestational diabetes. The description, so this is, there's two, they've offered two different options. So they've said according to one classification, if it's above 5.5 or the two-hour plasma glucose is equal to or greater than eight, then this is considered diagnostic of gestational diabetes. But there's an alternative diagnostic cutoff for gestational diabetes that was published later.
[9:27] And this is the contentious one is this one's got a lower cutoff. So if it's over 5.1 at the fasting one, if it's over 10 at the one hour or 8.5 at the two hour, then that could also be considered diabetes. So if I send a woman to get gestational diabetes testing, that'll give me the results for the test, what it showed. And then underneath it says it's got this big long disclaimer about the two separate diagnostic cut-offs that you could use to guide your diagnosis of gestational diabetes for this woman. So let's have a look at the evidence because this is what we're here for is to work out is what we're doing and recommending to women, does it have any basis?
[10:12] So Cochrane Database Systematic Reviews always like the mic drop journal that we can go to to answer a lot of these questions and because the oral glucose tolerance test or formal glucose tolerance testing is a medical intervention. It can be tested using randomized control trials. You can blind people to whether or not they have the glucose tolerance test or not. You can blind whoever's administering it. This is possible, entirely possible to do in a randomized control trial. And because it's a medical intervention and a medication in a sense, then it should be studied in this way. What does Cochrane say? So Cochrane's attempted to write an article on gestational diabetes testing multiple times.
[10:56] There was a 2010 one, there was a 2014. Now they've just updated it to 2017. And what they wanted to do was address the issue that to date, there's still uncertainty as to whether or not screening all women for gestational diabetes will improve maternal or infant health. So right off the bat, we don't know which technique is better, to screen everybody, to screen nobody, to screen everybody. Or to screen as an at-risk population. So the Cochrane database systematic reviews found only two trials.
[11:32] Randomized control trials, that were both done in Ireland. And this is important because ethnicity and diet and lifestyle and location has a big impact on whether or not you will get or be at risk of getting gestational diabetes. So they're both done in Ireland. The total population that was studied over these two randomized control trials was only about four and a half thousand women and they were both both the studies were found to have a moderate to high risk of bias so basically what they're saying is there's two studies they were kind of small there was a high risk that whatever they found was not accurate because the quality of the studies was poor now the cochran has basically said at the end of the whole paper they said there's not enough evidence to guide us on the effects of screening for gestational diabetes based on risk or where you do it, whether you do it at hospital, at a pathology lab with a GP, and we don't know the outcomes for women and their babies about glucose tolerance testing, if it accurately diagnoses diabetes, if doing it even improves outcomes for women and their babies, if it's capturing everybody who has diabetes, how many people are being left out. We have no idea whatsoever.
[12:48] Anything that's been done is culturally based, based on the setting and based on someone's preference they pulled out of their bot bot because there's no evidence. So I find it very hard to talk to my clients about gestational diabetes testing because I have to tell them that actually nobody knows what's better anywhere.
[13:09] Not me, not the hospital, not your DP, no one. We can't even decide what cutoffs we should use. No one can agree on what cutoffs should be used to diagnose gestational diabetes. So it's under-researched. So this is what, when I talk to people about this, and this is what gets a lot of attention on things like Instagram, they're like, it's just a test. It's just a blood test. What's wrong with doing it? Well, what's wrong with doing it is that we don't know if this test even works to diagnose gestational diabetes. No one's researched it properly enough that we can actually make conclusions that this is a helpful test and actually then for women who do get diagnosed with gestational diabetes based on this flawed system of diagnosing people.
[13:52] If they're in a midwifery program they will often be shifted off into the obstetric clinic and then all of a sudden they're on a pathway to be induced at 38 weeks because that's the policy regardless of if they've managed to control their diabetes or not and what I'd like to say here is is that if you do find that you're in a state where you have gestational diabetes if you've managed to so normally our insulin and our body and our blood cells will manage our glucose levels to a healthy level where you're not getting major highs and major lows if your body can't internally manage that, you can externally control that with diet. So if you've managed through your pregnancy to control your diabetes using diet control, your body and baby are completely unaware that you're in a diabetic state and you have effectively mitigated the risk of gestational diabetes.
[14:45] There is no issue in your body if you've charted all your blood sugars the whole pregnancy and you've had very few high readings after being diagnosed with gestational diabetes and your blood sugars are, say, stable and normal in inverted commas. Your baby and your body are unaware that you have gestational diabetes. You have effectively mitigated whatever risk this diagnosis presented you and you're, for all intents and purposes, a normal, well, healthy woman and in my opinion, should not be induced at 38 weeks just because it's the policy. Yes, I think there should be some interventions for women who have been unable to control their gestational diabetes in pregnancy. There are some risks to those women and babies, which again, not the topic of this conversation, but there might be a good reason to induce a woman who's got uncontrolled diabetes. In my opinion, there's no good reason to induce a woman who has gestational diabetes who's managed to control it with diet.
[15:43] Because they've managed to control it. They've mitigated the risk. So why are we still inducing them at 38 weeks? And so you've got to know that if you have this test and you do get diagnosed with gestational diabetes, but they happen to be also able to manage it, that doesn't matter to the usual hospital system. You're just on the same path as everybody else who's being diagnosed with gestational diabetes. So there's a massive issue and it's not around the screening. The screening test itself is probably pretty benign in terms of its impact on your body. The impact comes is the whole flow on effect of being diagnosed with gestational diabetes. This is creating a circumstance of unnecessary care for women and a potential
[16:26] over diagnosis of diabetes for women who don't have it. So for midwives who are sitting here going, my gosh, well, what do I do now? Because our hospital does universal screening. how do I counsel women about this we actually can only really say well that's the policy at this hospital unfortunately we don't have any evidence that supports use of this test for all women or we don't actually know anything about this test if it's an accurate one to diagnose diabetes or not so I mean there is an issue though some women do get gestational diabetes in their pregnancy so.
[16:59] The question remains is how do we find these women? How do we discover these women so that they can manage the diabetes and have a good outcome? Because there's no doubt that uncontrolled diabetes creates pathology in a pregnancy. We're not doubting that. We're saying if you do have diabetes, it's important that it gets diagnosed and it's important that it gets managed. What we don't yet know is the best way to diagnose it. formal glucose tolerance testing has not been proven to be the best way or the only way to diagnose gestational diabetes. So let's look at alternatives. Now that you've heard this and you think, well, I don't want the gestational diabetes test, but I would like to know if I have gestational diabetes. So those are two different things. So I can talk you through what I offer to my client. So if I look down that list of risk factors, you know, they have a first degree
[17:49] relative with diabetes. Potentially they're overweight. They've had a previous baby above 4.5 kilos, previous history of gestational diabetes. They're of an ethnicity that does put them at higher risk of gestational diabetes.
[18:02] And women who are older in their pregnancy. The other thing I also ask my clients about is their current diet. Do you actually have a high sugar diet or a diet full of processed foods? And if they say, actually, no, I eat really well. I really concentrate on nutrition, you know, we have a chat about all of that. So my other issue with gestational diabetes testing is that our bodies will actually adapt to the amount of sugar that we eat in our day. So people who have a high sugar or high.
[18:32] Simple carbohydrate diet with lots of processed foods, their pancreas will be trained to release and make more insulin than my body. What I would consider quite well, I don't have lots of sweet foods. I try and balance my carbohydrate intake with appropriate fats, proteins, and vegetables in order to balance my blood sugar levels. So I consciously eat that way. What I'm trying to say, my body is not trained to deal with high levels of sugar because and my pancreas isn't expecting it it's it's not thinking oh mel always eats a lot of sugar i really have to work my pancreas is chilling out every now and then mel over does it we'll deal with that when it happens but on the routine it's not so on that theory if i went for a glucose tolerance test my blood sugar i would expect it to be higher for longer than somebody whose body is used to processing sugar because my body's got to catch up. It's got to go, holy crap, she's had 75 grams of sugar. What the heck? We've got to get insulin out there. There's a delay in the process of managing that sugar. Whereas for somebody who has high sugar diet, their pancreas is ready, man. It's keen. It's ready. My theory is, and for my clients who propose to have a very healthy diet.
[19:51] I do talk to them about the possibility that they could respond to the glucose tolerance test as being diabetic because their body's not used to dealing with 75 grams of sugar. So what's an alternative? I have clients that are like, I do want to know if I have gestational diabetes, but I do not want the gestational diabetes test. So here's another option, which I feel, again, there's not evidence for this, but it's an option, theoretical option, just like the theoretical option of the oral glucose tolerance test. So what I suggest for women who want to have testing for gestational diabetes but don't want to have the glucose tolerance test, they can just test their blood sugar as if they were diabetic.
[20:30] So wake up in the morning, check your blood sugar. One hour after starting breakfast, check your blood sugar again. One hour after starting lunch, check it again. One hour after dinner, check it again. And then they can chart it. And if their blood sugar levels are over, so on the chart that I give women about charting their blood sugars, if after one hour after meals, if it's 7.4, over 7.4, then that's considered a reading too high. And if it's over 6.7 after two hours of eating, then that's also considered high. So they can actually self-monitor their blood sugar levels and make a diagnosis based on this real-time, real food circumstance.
[21:13] And so if after a week of testing, these women have not had a high reading above the certain ranges, and again, it's controversial what is considered a normal range and what's not, But if all of their readings for an entire week are completely normal, there's no way they could have gestational diabetes because if they had gestational diabetes, then that's represented by high blood sugars. And so in a way, you can tell if you have gestational diabetes by checking your blood sugar in real time with real food. That gives you real answers about what your blood sugar is doing during the week in pregnancy. So that is an alternative to formal glucose tolerance testing. Obviously that's something that could be negotiated in a situation where you have a private health care provider but in the chaotic busy large hospitals that are doing antenatal testing for everybody they might not have the capacity to deal with such an individualized approach but certainly for women if you feel like you are at risk of gestational diabetes if you think yes I would like to be screened but no I don't like the idea of oral glucose tolerance testing with this sugar drink.
[22:23] You can just buy blood glucose monitor equipment and check it yourself and be checking your levels with your healthcare provider to say, are these normal? Because if you don't have consistent ongoing high blood sugars,
[22:35] you do not have gestational diabetes. I'm not saying we shouldn't test for gestational diabetes because it's definitely an issue and we need a good strategy for how to identify the women who have gestational diabetes so that we can help them have healthy pregnancies by managing the diabetes. You know, we're doing all of this testing without actually knowing if it works. So I'm always looking for ways on how do I make sure I don't miss any clients who actually do have gestational diabetes.
[23:00] So there is this blood test that you can do. And actually this blood test, the HbA1c, is something that has been well known and tested and used for people who have diabetes in their usual life, not when they're pregnant. So there's heaps of evidence there for people who have type 2 diabetes. I'm not sure if they use it for type 1, but it's a long-term marker of how well-controlled someone's blood sugar levels have been. So if you've got a diabetic person who this GP is managing, for example, and they're on medication, and they do their HbA1c levels, and the HbA1c is super high, that's a clinical marker that overall they haven't been controlling their blood sugar levels appropriately, and so that can help dictate management processes. So more recently, they started trying to work out what is the cutoff range for HbA1c because we know that during pregnancy, your ability to digest and process and use sugar is altered. And so we can't just use the pre-pregnant research and just apply it to pregnant women because we already know that pregnancy is a completely different state when it comes to insulin and insulin resistance and blood sugar levels. So there has been a little bit of research on this. As far as I'm aware, if you do the HbA1c in the first trimester.
[24:19] Then that is an appropriate use and you can use... Pre-pregnancy levels to determine if a woman is diabetic. So if the HbA1c is within the normal range for a non-pregnant person.
[24:31] Then in the first trimester, then you can rely on that as an indicator of if somebody has pre-existing diabetes or a history of having high blood sugar levels even in the absence of diabetes. But I'm not aware if there's any good evidence of that in the second and third trimesters when there's already the impact of the placenta on blood glucose levels because I haven't looked into it enough but I certainly if I have an opportunity will offer women a HbA1c thrown into the usual antenatal blood screen as a way of building a picture of if this woman is at risk of gestational diabetes is there a history of high blood glucose levels is this someone who we should do further screening for as a pregnancy goes on this is new information to a lot of people it might not be new
[25:18] information to you five minute wrap up gestational diabetes is a problem. If you have uncontrolled gestational diabetes, there's no doubt in the evidence that that does result in poorer outcomes for you and your baby in the short term and the long term. So I think that we have a problem where we don't really properly know how to diagnose gestational diabetes. And so we've gone with this oral glucose tolerance test or this formal glucose tolerance test as a theoretical option for testing women and finding out if they have diabetes. The problem is, is there's no consensus on how to use this oral glucose tolerance test. What cutoffs can constitute gestational diabetes as a diagnosis?
[26:01] And we haven't yet done all the research on if this test is an appropriate test for gestational diabetes. However, we do have a problem that some women get gestational diabetes. And now clinicians and women need to decide what they're going to do about that because there's hospital policies, but there's no research that can really help guide what the best way to diagnose gestational diabetes is. 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. Follow me, Mel, @MelanietheMidwife on socials and the show @TheGreatBirthRebellion. All the details are in the show notes.
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