Informed Choices: Glucose Screening & Testing

Lets rewind from my last post on the GBS swab, which happens later in pregnancy, to glucose screening! This topic comes at an appropriate time, because I have seen a lot of confusion online about fasting and non-fasting glucose tests. There is even (honestly) confusion among providers at times I think – in terms of what instructions to give patients, so I will definitely be reviewing the general guidelines for this in addition to the screening itself and its risks and benefits (which are also very hot topics this year).

Disclaimer: this blog is for informational purposes only. This is not medical advice. Please seek medical advice from your trusted healthcare provider.

You can read about my experience with the Glucose Challenge Test (GCT) or glucose screening here.

What is glucose screening?

Between 24 and 28 weeks of pregnancy, you will be offered the option to complete a glucose test. If you have had a history of glucose in your urine or gestational diabetes in the past (there may be other risk factors that prompt this too), this test may be offered earlier in your pregnancy.

The initial test at this time is the Glucose Challenge Test (GCT), the 1-hour test. It is done to screen for gestational diabetes. The test will look at how your body processes sugar (glucose).

What is gestational diabetes again?

It is diabetes that occurs in pregnancy. Not the same as pre-existing Type 1 or Type 2 diabeteswhich have different management, considerations, etc. The mechanism is the same or similar though, in that your body during pregnancy cannot sufficiently produce insulin to manage your glucose levels.

Does this all sound like gibberish? Here is a basic video reviewing the pathology of gestational diabetes.

If you are diagnosed, this should be explained in-depth by your provider or specialist.

I’ll review the risks of gestational diabetes in the section below on risks and benefits of the screening and testing.

For the GCT, you will usually attend a lab and be asked to consume a 50 gram glucose drink (the “orange drink” infamously, however some places offer alternative flavours). The GCT is non-fasting so you do not need to book it at a specific time of day or fast prior to the test! Your glucose levels are then tested 1 hour after you have finished the drink.

Diabetes Canada has the guidelines for additional testing in a nice chart here. A value below 7.8 mmol/L would indicate a negative, while a value over 11.1 mmol/L would indicate a positive for gestational diabetes (please note these are the Canadian values and guidelines – I will include a link in additional resources for the American guidelines).

Values that fall in between these two numbers require additional testing (the Glucose Tolerance Test or GTT), which is the testing that is done fasting. Results are based on several ranges and can be seen here. Gestational diabetes is diagnosed if one of those results is above the recommended amount.

Alternatively, if you are high risk you may be offered the testing earlier and you may go straight to the fasting test (GTT).

In the US they offer the GTT as a 3 hour test (100 grams glucose) as well as a 2-hour (one-step, 75 g) test – both are usually fasting.

If you have questions about the instructions for your test, please ask your provider but I also recommend contacting the lab that you plan to attend.

Risks/Benefits of Glucose Tests

Many people are concerned about drinking a sugary drink and the risks this may present – especially for the 50 gram test, it is really similar to drinking many varieties of soda in terms of sugar intake. In particular, the orange flavour tends to taste like an orange soda or an orange Chubby if you remember those. Sugary drinks may make some people feel nauseated, light-headed or sweaty, so this is something to consider – though keep in mind these symptoms are fleeting.

Some people find the idea of the drink to be a bigger issue and want an alternative – there may be alternatives and you can discuss this with your provider. For example, a small study was done on the use of jelly beans as an alternative. The drink may also be skipped to pursue an A1C instead (this has been offered in the pandemic in some cases because of accessibility to a lab) – which is just a blood test that looks at the average of your blood sugar levels over ~3 months. However, it is considered less reliable for diagnosis when compared to the recommended glucose testing.

Some people may want to pursue self-monitoring of their blood glucosehowever this needs to be done consistently and multiple times – so it’s not, again, a recommended option (and will likely not be enjoyable for you).

Beyond these relatively minor possible side effects and personal considerations, the test poses little risk since it is just a blood test other than the drink. Some people may not like blood work – you should discuss this with your provider in advance, and with your lab if possible. There are things they may be able to do to make blood work more bearable for you.

Blood draws also may come with some risks for certain people such as excessive bleeding and fainting. If you know you have had these issues in the past, again, speak to your provider & lab tech prior to your test. Fainting can be managed by being prepared -ie. having you lay down for testing for example. There may also be a slight risk for infection and hematoma at the site where the blood is taken (some people are more prone to this, or it can be related to the administration of the test). Discuss any concerns with your provider and know that most of these are minor and/or manageable.

What are the risks of gestational diabetes?

The risks of gestational diabetes are of course the benefits of pursuing testing to identify it.

If you are diagnosed with gestational diabetes, different management techniques will be offered depending on your levels and other factors. Diet, exercise, glucose monitoring and sometimes pharmacological intervention (medicine) may be needed to manage gestational diabetes. You can read about the options and current evidence on the Diabetes Canada website.

We want to manage it because it poses risks (if unmanaged or undiagnosed) for our babies! Neonatal hypoglycaemia is usually the main concern – which is low blood sugar in your baby, which may seem confusing since in gestational diabetes moms sugar levels would be high. This is because, while they are still within mom, they experience these high sugar levels as well via the placenta. The baby’s pancreas responds by producing insulin to respond to these levels – so when baby is born and their own sugar levels are no longer high since they’re not shared with mom, it results in lower blood sugar because of the high amount of insulin. You can read more about the etiology of neonatal hypoglycaemia here.

Babies may also be born with “macrosomia“, which is essentially a larger baby. This can make birth more challenging at times and may mean that the birth requires more intervention. Baby may also have risks later in life for the development of Type 2 diabetes or heart disease.

You also face risks if your diabetes goes unmanaged and undiagnosed – such as the birth risks above, as well as an increased risk for pre-eclampsia which brings with it a host of other risks and challenges.

There are things you can do to prevent gestational diabetes from developing if you are high risk – nutrition consult is recommended by Diabetes Canada in early pregnancy (before 15 weeks). Early testing itself may help with early management and reduction of other related risks. Speak to your provider if you have concerns.

Additional Resources

SOGC – Glucose Testing

Diabetes Canada – Practice Guidelines for Diabetes in Pregnancy

StatPearls – Neonatal Hypoglycaemia

American Diabetes Association – Standards of Care & Management for Diabetes in Pregnancy

One thought on “Informed Choices: Glucose Screening & Testing

  1. Really, the best gift a child can receive is a healthy, properly functioning brain thus mind for life.
    Too many people will procreate regardless of their questionable ability to raise their children in a psychologically functional/healthy manner. Being free nations, society cannot prevent anyone from bearing children; society can, however, educate all young people for the most important job ever, even those high-schoolers who plan to remain childless. … I wonder how many instances there have been wherein immense long-term suffering by children of dysfunctional rearing might have been prevented had the parent(s) received, as high school students, some crucial child development science education by way of mandatory curriculum?


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