Glucose Tolerance Testing (GTT)

What is it?

Simply put, this is a check to see how your body manages to deal with the sugars in the foods you eat.


Because poor management of sugars can indicate that you have developed diabetes.


Diabetes in pregnancy is known as Gestational Diabetes, and if your BMI is 30+ you have an ‘identified risk’ for gestational diabetes. The likelihood is that health professionals you meet will bang on about it again and again.

The risk for bigger mums is often reported as being three times that of ‘women with a healthy weight’. Sounds worrying, doesn’t it?

But let’s look at some actual numbers before we panic.

One of the largest studies looked at more than 16,000 women and found that 9.5% of women with BMI 30+ had gestational diabetes, compared with 2.3% of women with a BMI under 30.

So yes, the risk is ‘considerably higher’ if you look at it compared to the figure for ‘normal’ sized women; it’s actually more than four times the amount. But 9.5% isn’t exactly astronomical, and it shows rather reassuringly that more than 90% of women with a BMI 30+ DON’T develop gestational diabetes.

You might want to keep this in mind, point it out even, if you feel a health professional is a little too much on your case, though you need to bear in mind that you’re at increased risk if you belong to certain minority ethnic groups (including people of African, black Caribbean, South Asian, Middle Eastern and Chinese family origin), or if someone in your close family has diabetes.

We always need to look further when we’re told that as larger women we have X times the risk of anything a ‘normal’ woman has, as it can be a way of health professionals railroading or panicking us into things; 3 x a small number can still be a small number!

But, because of this increased risk, both NICE and CMACE/RCOG guidelines recommend that women with a BMI of 30+ at their booking appointment should be screened for gestational diabetes.

Because the consequences of uncontrolled gestational diabetes can be quite severe, in some countries, all pregnant women have a glucose tolerance test, regardless of size.


You’ll be given an appointment for a clinic at somewhere around 24-28 weeks.

If you had gestational diabetes in an earlier pregnancy, you might be offered self-monitoring of blood glucose early in your pregnancy, or an early glucose tolerance test (at 16–18 weeks). If that returns a normal result, you will generally still be sent for a glucose tolerance test at 28 weeks to check again.


The test takes a couple of hours and is reasonably painless, if deathly boring.

Firstly, you won’t be allowed to eat anything from the night before.

The next morning, hungry and slightly grumpy, you’ll turn up at the hospital, where a receptionist will check you’ve not eaten anything for the required number of hours.

If you pass the test of being able to follow their instructions and not eat, you’ll then be directed to a room with lots of other hungry, grumpy, pregnant women, some of whom will be larger mums, but the majority will be there because they have another risk factor for gestational diabetes.

You wait your turn to have your blood taken, and when it’s finally your turn, the nurse taking the blood will check again that you’ve definitely not eaten anything.

This may make you feel a bit like snapping that just because you’re overweight doesn’t mean you’re incapable of going without food for a few hours, but try not to be offended, they check this with everyone as there is no point in doing the test if the person hasn’t been fasting beforehand.

A small amount of blood will be taken and your blood glucose level will be checked to give a base line reading.

You’re then instructed to drink a large cup of not terribly pleasant sugary squash. You need to drink this quite quickly, preferably down in one. The squash contains a measured amount of glucose (sugar), and the test will check your body managed to deal with it in a reasonable amount of time.

So you then have to sit around on whatever uncomfortable chairs are provided in the waiting room for 2 hours. You aren’t allowed to go for a walk to ease the boredom (this would speed up how your body processes the sugar), and you’re certainly not allowed to eat or drink anything else while you wait as this would mess up the test because you would have had more than the measured amount of sugar they are expecting your body to have to deal with.

Time will pass slowly.

Eventually your name or number will be called and your blood will be tested a second time. You may get the result there and then, or some hospitals say they will only contact you if they suspect you have a problem (how would they notice if they lost the test? Who knows!?)

Anyway, now you are free to go and eat something! If you’re a prepared sort of person, now would be a good idea to pull that snack you brought with you out of your bag to make all the rest of the poor, hungry, grumpy waiting mums jealous.

Any reason not to?

People who don’t like needles might want to put off this test, but it really should be quick and reasonably painless as the nurse taking the blood should have had lots of practice!

Some women feel sick and dizzy as a result of not eating for that length of time.

After having not eaten for that length of time the glucose solution makes some women vomit, particularly if you’re taking any anti-emetics (anti sickness medication) for acute morning sickness (Hyperemesis Gravidarum) as you won’t be able to take them beforehand.

Book Cover - Ina May's Guide To Childbirth

There is some thought in well-respected quarters (Ina May’s Guide to Childbirth for one) that the test is unreliable, and therefore puts the mum and baby under unnecessary stress for no concrete benefit.

Like all medical interventions, you don’t have to take the Glucose Tolerance Test, although your doctor will likely really encourage you to do so (for that read ‘get a bit stroppy when you say you don’t want to do it’) as Gestational Diabetes can cause some pretty nasty complications.

Strictly speaking it’s their job to ‘offer’ the test and up to you to accept or refuse, but they don’t always see it that way!

I have sadly heard on more than one occasion of larger mums being made to take the test up to eight times because the healthcare professional responsible for their care doesn’t believe the negative test result. This is not acceptable – the test is time consuming, isn’t particularly pleasant, puts unnecessary stress on your body and presumably your baby, and if they don’t trust the result, where’s the benefit of doing it repeatedly with the hope of getting a different result!? 90% of obese women don’t develop GD. The test is more than likely going to be negative.


For many women identified as having gestational diabetes, the treatment is a reduced sugar diet, so some women choose to eat a reduced sugar diet as a precaution, keep an eye out for other symptoms and not take the test.

Of course, this wouldn’t help if you were one of the few people for whom a reduced sugar diet was insufficient and insulin was necessary to control your blood sugar, and not all women experience symptoms. Uncontrolled blood sugar can have serious consequences for you and the baby, so it shouldn’t be ignored. For more information, have a look at Gestational Diabetes UK’s website.

Some women who have refused to take the GTT have been offered instead to have a fasting blood test taken first thing in the morning, checking blood sugar levels and HbA1c. This still involves needles and fasting overnight, but only one blood test, no thick, syrupy drink and much less sitting around in a hospital all morning getting hungrier and grumpier.

Since 2015, women are diagnosed with gestational diabetes if they either have a fasting plasma glucose level of 5.6 mmol/litre or above, or a 2-hour plasma glucose level of 7.8 mmol/litre or above, according to NICE.

So if you find a consultant willing to do a fasting blood test as a compromise, they might set a lower threshold than 5.6mmol/litre as a trigger to send you for a full GTT. Perhaps something above 5.0mmol/litre would warrant further investigation by GTT.

During the first trimester of pregnancy, the HbA1c target for women with diabetes is 43 mmol/mol (6.1%) or lower. During the second and third trimesters of pregnancy, from week 13 onwards, HbA1c should not be used for assessing blood glucose control, so your consultant may be less interested in this if you’re past 13 weeks gestation. Source –

You could offer to self-test your glucose on a daily basis for a time, to check your sugar levels instead (this still involves needles, though).

Given that taking the GTT only takes a few hours and is only mildly uncomfortable and inconvenient, it’s probably easiest to suck it up and do it. It will provide you with reassurance at the very least. But if you’re being pushed to take the test more than once, with no other identified reasons other than your weight, you might want to heavily question the biases of your Health Care Professional, perhaps suggest they read this:

How to be a Plus-Size-Friendly Professional


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