The Glucose Tolerance Test (GTT)

Photograph copyright Angela Martin Redboots Photography

The Glucose Tolerance Test (GTT) is a common test performed in pregnancy. The GTT may be suggested to you if your health care provider thinks you fall into risk groups for developing gestational diabetes or if you are showing symptoms of gestational diabetes in your routine clinical checks.

Gestational Diabetes – What is it and how does it affect you and your baby?

Gestational diabetes is a type of diabetes that you get in pregnancy.
You do not need to be a diabetic to develop gestational diabetes.

Gestational diabetes is when you have a high level of sugar in your blood due to chemical changes in your body during pregnancy.

When you eat, your digestive system breaks down your food and converts it into a sugar called glucose. The glucose enters your blood stream. Your pancreas secretes a hormone called insulin. Insulin works with glucose to create fuel for your cells. With diabetes, your body is not able to make enough insulin to convert the glucose to energy and as a result, your blood will show high levels of sugar. Hormones in pregnancy can sometimes change the way our body produces or reacts to insulin. For most women, the pancreas simply makes changes to keep up with these demands. However, if this does not happen, sugar levels rise in the blood, resulting in gestational diabetes.

Between 2-5 in 100 pregnant women will have gestational diabetes. (HSE)

There are often no symptoms with gestational diabetes, however, some women may experience extreme tiredness or routine clinical urine tests may show sugar is present.

If not controlled, gestational diabetes can cause serious complications for you and your baby such as:

* placenta abruption – when you placenta comes away from the wall of your womb
* premature birth
* macrosomia (your baby measures larger for dates): the excess glucose in your body is passed on to your baby
* shoulder dystocia
* you are at risk of developing diabetes later in life or in a future pregnancy
* your baby is at a greater risk of developing diabetes later in life
* your baby is at a greater risk of obesity
* feeding problems for your baby
* low glucose/sugar blood levels in your baby (hypoglycaemia)
* jaundice
* respiratory problems in your baby – your baby has problems breathing
* pre-eclampsia
* high blood pressure
* increases risk that your health care provider may recommend inducing your labour before your due date
* increases your risk of assisted delivery or Caesarean section
* increased risk of death for mothers and babies as compared to non-diabetic women.

If you are diagnosed with gestational diabetes, you will be asked to monitor your blood sugar levels from home. Managing gestational diabetes can reduce severe complications to your baby and can make women less likely to require Caesarean section or assisted delivery.

Gestational diabetes can be effectively controlled with a balanced diet with healthy low GI options and regular exercise like swimming or walking. It is important to eat regular, balanced meals made with fresh produce. Speak to your health care provider for an appointment to meet with a nutritionist.

More information on GI foods here.

Some women may be required to use insulin to control their diabetes. This is suggested when changes to your diet and exercise have not managed glucose levels. Once you go on insulin, you will be required to take it for the duration of your pregnancy. Insulin should be prescribed on an individual basis, to meet your specific demands. Insulin is generally accepted to be safe to use in pregnancy, however, as with all medications, there can be side effects or reactions to some drugs. Make sure you discuss this with your health care provider if there is something you are concerned about.

Most women will no longer have diabetes or require insulin once their baby is born.

Additional Costs: Irish Government Drops Aid to Women with Gestational Diabetes

In August 2013, the Irish Government dropped gestational diabetes from the long-term illness scheme in the HSE (Health Service Executive). This means that women whom have been diagnosed with gestational diabetes and require insulin to control their glucose levels no longer qualify for aid to cover these costs.

“The HSE are doing this purely to save money and without regard for patient safety, quality of care and outcomes . . . There will be a catastrophe for a mother or a baby,”

Prof Fidelma Dunne, Irish Times, Aug 6 2013

The long-term illness scheme previously supplied women with the necessary tools to monitor and control their diabetes. Without this aid towards costs, women will be required to pay €40 per week for medically necessary supplies.

What is the Glucose Tolerance Test (GTT)

GTT is a test performed at your antenatal clinic to see how your body breaks down sugar.

The GTT is usually performed around 28 weeks into your pregnancy. If there is a concern that you have developed gestational diabetes prior to 28 weeks, for example sugar is present in your urine, you may be recommended to have the GTT prior to 28 weeks.

The GTT takes several hours to complete. It requires several blood tests, fasting, and you will be asked to drink a high glucose drink.

HSE’s guidelines on Glucose Tolerance Test:

* You will be asked to eat your normal diet prior to the test
* You will be asked to fast for 12 hours prior to the test (no food or fluids except water)
* You should not smoke prior to the test
* A fasting blood sample will be taken
* You will be asked to drink a sugary drink (lucozade)
* You will be asked to sit quietly and relax
* Your blood will be taken 1 hour after drinking the lucozade
* You blood will be taken 2 hours after drinking the lucozade
* Your sugar levels in your bloods are then compared. Bloods outside of accepted measures are considered diabetic.

HSE Guidelines:Guidelines for the Management of Pre-gestational and Gestational Diabetes Mellitus from Pre-conception to the Postnatal period (2010)

Who is recommended to have the Glucose Tolerance Test?

In Ireland, screening for gestational diabetes is selective, not routine. This means that recommendations for screening are made for groups of women who are considered of a higher risk of developing gestational diabetes, rather than screening ALL women. At your booking appointment, a midwife will take your history. If you fall into any of the selected risk groups, you will be recommended to have a GTT.

You will be recommended to have the Glucose Tolerance Test if you fall into any of these groups:

* Have a previous pregnancy with gestational diabetes
* Have a previous ‘big’ baby (at or over 4.5kgs – 10lbs)
* Have a BMI over 30
* You are aged at or over 40 years old
* A family history of diabetes (first degree relative)
* A previous pregnancy resulting in the death of your baby
* If you have been on long-term steroids
* PCOS (Polycystic ovary syndrome)
* Polyhydramnios (high fluid levels) and/or macrosomia (baby measuring ahead of dates – big) in existing pregnancy
* Ethnicity from following Countries: India, Pakistan, Bangladesh, Black Caribbean, Saudi Arabia, United Arab Emirates, Iraq, Jordan, Syria, Oman, Qatar, Kuwait, Lebanon, Egypt
* if routine clinical checks suggest you may have diabetes – urine samples tests positive for sugar or baby measuring very big

Advantages of the Glucose Tolerance Test

* The GTT is considered the most effective way to determine if you have gestational diabetes

* Early detection of Gestational Diabetes gives you a better chance of monitoring your sugar levels

* Managing your sugar levels early decreases the risks to your baby

* Managing your sugar levels early decreases the chances of your baby growing larger for dates

* Managing your sugar levels may decrease the risk of interventions in labour and birth

Disadvantages of the Glucose Tolerance Test:

* There are no serious direct risks to the GTT, however, some women report dizziness, fainting, vomiting, due to fasting and/or the use of a high sugar glucose drink on an empty stomach.

* Fasting for 12 hours in pregnancy can be difficult.

* You may receive soreness or a bruise at the needle cite.

* If your blood results come back positive or borderline for gestational diabetes, you will be closely monitored in pregnancy and attend a diabetes clinic.

* You will not be eligible for midwife led care options such as homebirth or MLU if have gestational diabetes.

* You may be recommended for induction before your due date.

As with all tests, treatments, and procedures, you will be required to consent to have the GTT. You may be happy to consent for the GTT. Or prefer to wait to have a GTT until there are warning signs that diabetes is present. Or decide not to have the GTT at all. Your care team should go through all the benefits (the advantages of GTT screening), the risks (the disadvantages of GTT screening), implications (associated risks) and possible future consequences, in order for you to make an informed decision.

Even if the GTT has been recommended for you, it is your decision. You may opt in, opt out, or do nothing (wait and see). It is up to each woman to consider all the information in order to make the best choice for her and her baby.

You can read more about informed decision making and tools to help you communicate here.

What Women Say:

“I was recommended to have a GTT on my 5th pregnancy. I had never been asked to have one before, but they had recently changed the guideline so I now fell into a ‘risk’ group. My weight was the same as it had been on other pregnancies, no history of big baby, never had sugar present in the urine or any other complications associated with gestational diabetes so I declined the test saying that I would have it if there was a medical need but not due to selective screening. The midwife in ante-natal booking was surprised and didn’t take it well, but I was supported by the consultant at a follow up appointment. It was agreed that if at any point we felt there was a medical need to have the GTT, we would revisit the issue. There never was – baby measured bang on, no large weight gains for either of us, never any sugar or protein in urine, etc.”


“I felt it was an unnecessary test because ultimately I didn’t have diabetes. I had the test because at 32 weeks my baby was measuring big and I had a +1 urine sample. I had no other symptoms such as tiredness and thirst. My consultant said it was necessary but funnily the midwife booking the test for me took one look at me and said I didn’t have it! She just asked did I have breakfast that morning – which I did- and said that was the reason for the +1. It was a very tough test to take at 32 weeks- fasting from midnight and no drinking was pretty hardcore. Taking of blood was quite uncomfortable- there were four samples taken. The best bit was chatting with the other women in the waiting room ,who were super nice , and hearing their baby stories and the tea and sandwich afterwards…..starving”


“I had what I think was glucose intolerance, didn’t believe it was diabetes. I was putting out glucose in my urine in all my 3 homebirthed babies (can’t remember on my first) but made changes to my diet-on strict instructions from my midwife-and managed to keep it under control. Never had a GTT although if the hospital knew I reckon I would have been asked to have one. I wonder if the criteria is too strict (but that’s only personal supposition, not based on any research, as I haven’t looked it up at all).”


“I have reservations about the GTT – I had 3 kids over 12 years and it was unheard of during my first 2 pregnancies to hear of having it done. Now everyone seems to be recommended to have it. I have a friend who was told she had diabetes even though she was borderline results. She was on insulin and induced at 38 weeks as there were concerns the baby was measuring large. Baby was born via section for failure to progress and weighed in a ‘massive’ 7lbs 1oz at 38+4 weeks.”


“I don’t understand why anyone would refuse to have this test…I don’t like needles either but surely your baby is worth the discomfort of the test!”


“It never occurred to me that I could decline to have the GTT – there was never an opportunity. I was simply flagged due to my age (40) at booking and a date was given to me there and then for the GTT. No information, no chat, nothing. Just told to show up.”


“I was flagged to have the GTT when I booked in during mid pregnancy as my bmi fell into risk groups. The thing is, I work really hard to be healthy in pregnancy to avoid complications like diabetes. I cut out all sugar and am active. I have never had a glucose drink in my life – pregnant or not! So why on earth would I agree to starve myself for 12 hrs and then subject my body and my baby to pure glucose? Would you give Lucozade to a pregnant woman or a newborn? I think not! My second issue is that I was not booked in until I was nearly 19wks pregnant! It was on THAT booking that my BMI was taken….I obviously had put on normal pregnancy weight at that stage. I refused the test and had a perfect pregnancy and gave birth at 41+2 to a perfect 7lbs 9oz baby boy.”


“Like everything, its an individual decision and whatever a woman decides should be respected. I believe very little information is provided to women prior to booking at GTT – which means women are not having the opportunity to make an informed decision. For me personally, I will only consent to that which is required due to medical indication – necessary intervention. This is not only during labour/birth but also pertains to all tests in pregnancy or after. If there is a genuine medical NEED for a test or intervention, I expect to have this discussed with me in order to come to a decision and a plan of action. But there rarely is medical indication for these tests. And the criteria has been widened to catch more women, which means that women are being treated for diabetes who perhaps shouldn’t be…. High risk clinics and status has serious implications on how your pregnancy, labour, birth, and post natal care is managed and it completely kills any limited choice you may have on place of birth. All these factors contributed to why I chose to abstain from the GTT and all other tests where no medical indication”

Urine Tests to predict Gestational Diabetes

In your pregnancy, you will be asked to provide a fresh urine sample at every ante-natal appointment. Your sample should be collected in a clean dry container and should be from mid-stream urine. To do this, you wee for a few seconds and then collect your sample. Most GP surgeries and clinics have a supply of sterile pots for urine samples. Make sure to pick a few up at each appointment!

Your urine sample will be tested at each appointment and provides your health care provider with important clues to ensure that your pregnancy is healthy.

To test your urine, your health care provider will take a plastic dipstick and place it into your urine sample. This ‘dipstick’ tests your urine for:

* protein – having protein in your urine can be a sign of an infection. In late pregnancy, protein in your urine, with high blood pressure, can also be a sign of pre-eclampsia. Pre-ecampsia is a serious condition in late pregnancy. Other symptoms include blurred vision, headaches, and swelling of your face and hands.

* nitrates & white cells – these can show if you have an infection like a UTI urinary tract infection. If your urine is positive for nitrates and/or white cells, your urine sample will be sent to a lab for testing. The reason for this is that some bacteria which cause infections can be linked with premature birth

* glucose – if there is sugar (glucose) in your urine, it can be a sign of gestational diabetes. It can also mean that you have eaten something very sugary just before you provided a sample.

Urine dipstick tests can show if glucose is present in your urine. This can be a marker for Gestational Diabetes. The most reliable way to diagnose Gestational Diabetes is having the GTT. If you urine tests positive for glucose on two occasions, you will be recommended to have an oral Glucose Tolerance Test.

Concerns with Guidelines?

The HSE National Guidelines for Gestational Diabetes in Ireland was recently revised to widen the diagnostic criteria for gestational diabetes. This means that a more women will be diagnosed with gestational diabetes – women who previously would not have been diagnosed as being diabetic.

Some research has highlighted concerns with the new criteria. This research suggests that due to wider criteria there is a significant increase on infrastructure. The demand of more women effects antenatal clinics, high risk clinics, diabetic clinics, and means women have longer waiting times and less time with obstetricians.

It also suggests that there is no clinical benefit for widening criteria – that women are being treated for diabetes without evidence.

The research states:

“The new diagnostic criteria for GDM will result in an increased rate of diagnosis of GDM and therefore increased surveillance of these patients. However this treatment will not improve perinatal outcome, we may now be diagnosing and treating a group of women without sufficient evidence of clinical benefit.”

Read more here:

Preventative Measures

A healthy and balanced pre-pregnancy diet and regular exercise, particularly ‘vigorous’ exercise has been shown to protect women from gestational diabetes.

Research has also shown that weight gain between pregnancies has been shown to be a factor in gestational diabetes. Women who put on a significant weight gain (3 BMI units) were double at risk of developing gestational diabetes in their subsequent future pregnancy.

Recommended Reading:

Gestational Diabetes and the Glucola Test

Associations of Physical Activity and Inactivity Before and During Pregnancy With Glucose Tolerance “Physical activity, especially vigorous activity before pregnancy and at least light-to-moderate activity during pregnancy, may reduce risk for abnormal glucose tolerance and GDM.”

Gestational Diabetes, HSE


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