BLOOD GLUCOSE REGULATION IN PREGNANCY
An alarming number of pregnant women are diagnosed with gestational diabetes in Australia (more than 1 in 6). The inordinate amount of women diagnosed from doing one standalone test is something I have questioned as a practitioner, and now as a pregnant woman myself. From the inconsistent acceptable blood glucose ranges (UK vs. Aus - old vs new ranges; criteria changed in 2010 since which GDM diagnosis has skyrocketed) to the poor reproducibility of the oral glucose tolerance test (OGTT), I do ponder if this is even a worthwhile test for well, healthy women with no risk factors for diabetes. Is this causing more stress to pregnant women than is necessary? From my experience with my patients, the answer to this question could be yes.
Glucose regulation in PREGNANCY
During pregnancy, there is an increased demand for glucose to support the growing baby and adaptations take place to ensure glucose homeostasis. Essentially, a pregnant woman becomes more insulin resistant as pregnancy goes on (placental hormones play a role in this change), meaning insulin is less responsive to glucose. The pancreas anticipates this change and over time will increase its β-cell numbers to accommodate. There is no question that this needs to be a well-regulated process—too little or too much glucose both come with complications.
In GDM, this pancreatic β-cell adaptation does not seem to take place and β-cells are dysfunctional, lending to even greater insulin resistance than is healthy for pregnancy. The cells that secrete insulin are no longer responding to glucose appropriately, which then means glucose concentrations elevate and remain elevated for a prolonged period of time (glucose uptake is said to reduce by up to 54% in GDM). Bub’s pancreas then must deal with high levels of glucose by producing its own insulin. Over time, if glucose is continually spikey or high, it can impact long term genetic predisposition for glucose and insulin issues for bub later in life.
Testing blood glucose in pregnancy
The mainstay test for glucose tolerance in pregnancy is the OGTT. A woman’s glucose levels are taken fasted, then she drinks 75g of glucose, and 1-hr and 2-hr readings are taken thereafter. If all levels are within healthy range, then all is well. Though, women are diagnosed with GDM purely on this test alone, even with marginally increased levels (and sometimes only the fasted level). How many of these women truly have pathophysiological GDM and need management? The alternative is to opt out of this test, choosing to do either manual glucose tracking over 4-14 days with your usual diet, writing down your levels, or using a continuous glucose monitor (CGM) to track trends in glucose against healthy ranges. There are benefits to this, in that, you are then able to see how well you are going with glucose management as a whole.
What we need to take into account with blood glucose readings
There are many outliers in terms of where our glucose sits that can be unrelated to food and I want to mention a few here:
- Cortisol Awakening Response (CAR) or ‘dawn phenomenon’
When we wake up, our body mobilises blood glucose for us to get going. For women who are made to track their fasting levels after GDM diagnosis, this can be a real kicker. We might see a slight rise in blood glucose upon getting up in the morning, which will usually come back down within the hour. For me, I notice that my ‘fasted’ blood glucose is <5.0mmol/L within 30-35 mins of waking up (or getting up earlier to go to the bathroom!). This is so important when it comes to tracking our glucose so we don’t get in a tizzy thinking we have diabetes of a morning reading that is actually related to cortisol. Why I love the CGM is you can see this transient nature of the morning reading and watch it rise, then fall.
This is something to take into account if you do choose to do the OGTT. If you only just recently got out of bed, you may indeed see a higher ‘fasted’ glucose reading, which could be related to your CAR.
- Stress in general
With stress, cortisol increases, and just like CAR, increases in cortisol can mobilise glucose. This is in case we need to fight or flight—we have the energy to do so in the form of glucose. Again, if you wake to a screaming baby, or you are reading emails that are giving you overwhelmed vibes, or you are suddenly shocked (like slamming on your breaks whilst driving), testing glucose thereafter may indeed negatively influence your results.
I always recommend my pregnant women who are doing the OGTT to cancel the test if they have had a stressful morning, something happens on the drive there (like slamming on breaks), and once arrived listen to a calming meditation or music, read a book etc (no instagram, or social media, get off emails etc etc). You want to be in a super calm state.
But this is the same if you are seeing a spike in glucose if you are using a CGM or manual tracker. Take into consideration how stressed you are. Caffeine/coffee can also mobilise glucose via increases in cortisol (I personally don’t see this effect, so don’t believe it happens for everyone). Something to consider though!
- Physical activity
When we exercise, we will also see a spike in glucose as the body adapts to physical movement and the increased need for glucose. Over time this may come down. For me, I actually notice my blood glucose go quite low in movement and so I have found having ½ an orange helps to bring it back into range so I can finish safely.
In summary
The OGTT is not the only way to assess glucose regulation and tolerance in pregnancy. Be mindful this test is taken in a figment of time, and many outliers can impact levels (especially your fasted level). We have seen a stark rise in GDM diagnosis since the testing range standards dropped in Australia. Has this been useful, or more of a hindrance for otherwise well, healthy pregnant women?
I do urge you to consider what is right for you—whatever you decide is the best decision. It is to be duly noted that if a GDM diagnosis is given, you can track your glucose with a CGM or manual reader to better understand where things are sitting (and put your mind at ease). It’s great to have back up data to avoid unwanted intervention later on in pregnancy, that (in my opinion) can be unnecessary. See part 2 of this series for more of my experience using a CGM.