Diagnosing gestational diabetes

In this post, I share risk factors and methods of diagnosing gestational diabetes in the United Kingdom and Ireland.

What is gestational diabetes?

Diabetes is caused by too much glucose (sugar) in the blood. A hormone called insulin controls the amount of glucose in the blood.

During pregnancy, the body produces several hormones, such as oestrogen, progesterone, and human placental lactogen (HPL). These hormones make the body insulin-resistant, which means the cells respond less well to insulin, and the level of glucose in the blood remains high.

The body should produce more insulin to cope with the increased amount of glucose in the blood. However, some women either cannot produce enough insulin in pregnancy to transport the glucose into the cells, or their body cells are more resistant to insulin. When this happens, blood glucose levels remain too high. This is known as ‘gestational diabetes mellitus’, which can also be defined as carbohydrate intolerance.

Gestational diabetes is usually diagnosed by having an OGTT/GTT (oral glucose tolerance test) between 24 – 28 weeks; however, women showing symptoms or those that have higher risks of developing gestational diabetes may be tested earlier.

Gestational diabetes affects around 5% (5 in every 100 pregnancies) in the UK

What is the main impact of gestational diabetes?

With gestational diabetes, when too much sugar remains in the mother’s bloodstream, it is passed through to the baby. The baby then has to increase its own insulin production to help process the excess sugars.

Insulin is a growth hormone, and the result is that the baby’s AC (abdominal circumference) increases. The overproduction of insulin causes adipose tissue (subcutaneous fat) to form, which makes the baby ‘big’.

Controlling blood sugars with diet, exercise and some will also need meds/insulin, this helps the baby to regulate their insulin production to normal levels and the rate of growth of the baby’s AC slows whilst the rest of the baby’s growth catches up. This means that the baby returns to a ‘normal’ growth size.

Are some women at a higher risk of getting gestational diabetes than others?

 You have an increased risk of gestational diabetes if:

• your body mass index (BMI) is 30 or more
• you have previously had a baby who weighed 4.5kg (10lbs) or more at birth
• you had gestational diabetes in a previous pregnancy
• you have PCOS (polycystic ovarian syndrome)
• you have a family history of diabetes – one of your parents or siblings has diabetes
• your family origins are South Asian, black Caribbean or Middle Eastern
• you are aged 35 or older

Risk factors for diagnosing gestational diabetes

Obesity is mentioned in the media a lot with regards to gestational diabetes, and there is a stigma attached to GD diagnosis that only obese or unhealthy women get diagnosed. Sadly, this means that many women feel it is not necessary to be tested because they are not overweight, or those who are diagnosed feel embarrassed or ashamed that they have caused this complication.

We see so many mothers joining our Facebook support group who are not overweight, so I wanted to conduct some research from our members on risk factors linked to diagnosing gestational diabetes.

In 2024, I conducted a Google Forms survey for patients diagnosed with Gestational Diabetes. Here are the results of the risk factors in 3,270 women diagnosed with GDM:

Obesity as a risk factor for gestational diabetes

Obesity [BMI of 30+] was found to be the most significant risk factor, with 1,784 or 54.6% of 3,270 respondents being diagnosed as having gestational diabetes.

Obesity is the only risk factor that the mother can impact before pregnancy. The rest of the risk factors are genetic or simply cannot be helped, and so it could be for this reason that we see so much press around obesity and gestational diabetes risk.

It should also be noted that although a BMI of 30 or more was the biggest risk factor found, in our survey of 3,270 women, just under half (45.4%, 1,486 women) did NOT have a BMI of 30 or more.

In this photo, you can see Helen at 35 weeks pregnant who often had people commenting how she could have gestational diabetes being so slim, even medical professionals! One consultant said, “I don’t understand why you were tested; you don’t look like you would have GD”.

Sadly, Helen is just one of many who have experienced these kinds of comments and confusion. If we have medical professionals with this sort of opinion and presumption, then no wonder we are faced with such challenges over gestational diabetes diagnosis.

No risk factors for gestational diabetes

How many women could be going undiagnosed and suffering the consequences of gestational diabetes if we have seen a result of 11.5% of women having none of the noted risk factors? This figure could, in reality, be much higher as these women are simply not getting screened because, in many areas, only women with the above risk factors are screened.

It is often the case that we see women being screened for future pregnancies following the birth of a previous large baby or following a birth which was complicated with shoulder dystocia. On reflection, most of the women I see coming to my support group in these future pregnancies very often comment that they feel their previous pregnancy was undiagnosed GD.

It is for this reason that I believe that all pregnant women should be offered the screening test for gestational diabetes, not just the higher-risk groups.

Reducing the risk of gestational diabetes

Research^​2–4​ has shown that diet and exercise in those who have a high BMI before pregnancy could reduce the risks of developing gestational diabetes.

Research has shown the following for women who are overweight (BMI > 25) or obese (BMI > 30): If they didn’t change their diet, 16 out of 100 women were diagnosed with gestational diabetes. If they did change their diet, 6 out of 100 women were diagnosed with gestational diabetes.

Studies on women with a normal weight found the following: 5 out of 100 women who didn’t get much exercise were diagnosed with gestational diabetes, compared to 3 out of 100 women who exercised more.

What can help prevent gestational diabetes?  Institute for Quality and Efficiency in Health Care (IQWiG)

Symptoms of gestational diabetes

It is very common for no symptoms to be present and this is why many ladies feel that they can’t possibly have gestational diabetes after receiving a positive result and struggle to come to terms with the diagnosis.

Some women may experience some symptoms such as:

• Headaches
• Blurred vision
• Feeling thirsty
• Feeling shaky or unsteady
• Nauseous when needing to eat
• Urinating more frequently
• Tiredness
• Recurrent infections, such as urinary tract infections (UTIs) and thrush

You will notice that many of these symptoms are common during normal pregnancy so it is hard to determine if they are due to gestational diabetes or just pregnancy itself until a glucose tolerance test is performed.

If you have any of the above symptoms, you should enquire about being tested for gestational diabetes.

Diagnosing gestational diabetes in the UK & ROI

For women with any of the above risk factors, a 2-hour 75 g oral glucose tolerance test (OGTT or GTT) is used for diagnosing gestational diabetes between 24 – 28 weeks.

If glycosuria (glucose in the urine) of 2+ or above on one occasion, or of 1+ or above on two or more occasions is detected by urine dip test during routine antenatal appointments, this may indicate undiagnosed gestational diabetes and so women with this should be referred for an OGTT.

In some areas, all pregnant women are screened for gestational diabetes.

Those who have previously been diagnosed with gestational diabetes are often tested at 16 weeks in subsequent pregnancies and again at 24 – 28 weeks should the first test come back negative.  Some hospitals will not test for gestational diabetes in subsequent pregnancies and may offer blood glucose monitoring from an early gestation instead.

What is an Oral Glucose Tolerance Test (OGTT or GTT)?

This is the test used for diagnosing gestational diabetes in the UK & ROI.

The test involves fasting (not eating or drinking) from the previous night, having a fasting blood test taken on arrival, drinking 75g of glucose (this may be in the form of a glucose syrup drink), and a subsequent post-glucose blood test taken after 2 hours.

You should check with your hospital when you should fast and whether you can drink water during this time.

All hospitals can vary the targets used for diagnosis of the OGTT.  Some will take three blood tests (fasting, one hour and two hours post glucose), whereas others will take two (fasting and one-hour post glucose).

In some areas, they may use a fasting glucose test alone or an HbA1c blood test instead of an OGTT.

Diagnosing gestational diabetes during the Covid-19 pandemic

Due to the Covid-19 pandemic, in 2020 RCOG recommended that the HbA1c test is used for diagnosing gestational diabetes. This is because the HbA1c test is one simple blood test which can be taken at any time of day, rather than having patients waiting around at the hospital for over two hours in clinics.

The HbA1c blood test shows an average blood glucose level over a three-month period.

Unfortunately, as this test is the average blood glucose over a long period of time, if blood glucose levels have only risen towards the end of the three-month period, it will still only show an AVERAGE blood glucose and therefore may cause a false negative result when actually the mother has developed gestational diabetes.

Research^​5,6​ has shown that using the HbA1c to diagnose gestational diabetes during the pandemic failed to detect gestational diabetes in over half of the women:

In our setting, the RCOG Covid-19 gestational diabetes screening regime failed to detect 47 of 82 (57%) women subsequently identified as gestational diabetics, and therefore cannot be recommended for general use.

Impact of changes to national UK Guidance on testing for gestational diabetes screening during a pandemic: a single-centre observational study

The Postcode lottery in diagnosing gestational diabetes

Depending on where you live, you may or may not be screened for gestational diabetes during pregnancy.

Some NHS Trusts screen all pregnant women for gestational diabetes and offer a blood glucose test at 8-12 weeks of pregnancy, but this is not the case in all areas.

In most areas, only women with known risk factors are screened, and the risk factors used can also be different.

Different target levels are used for diagnosing, which also poses problems too.

Some women may be referred for testing if they have symptoms of gestational diabetes, but unfortunately, this is not the case for all.

Diagnosis test target levels in England & Wales:

NICE guidelines (recommendations for England & Wales) for diagnosis are the following:

1.2.8 Diagnose gestational diabetes if the woman has either:

• 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. [new 2015]

Diagnosis test target levels Scotland:

SIGN guidelines (recommendations for Scotland) for diagnosis are the following:

2.3 Gestational diabetes
The diagnosis of GDM is made using a single-step 75 g OGTT when one or more of the following results are recorded in those with risk factors during routine testing:

• fasting plasma glucose ≥5.3 mmol/L
• (one-hour post 75 g oral glucose load ≥10.6 mmol/L, where used)
• two-hour post 75 g oral glucose load ≥9.0 mmol/L.

HbA1c in early pregnancy (first trimester) should be considered to detect overt diabetes in pregnancy and to identify a cohort at risk of GDM.

• Women with HbA1c ≥48 mmol/mol should be diagnosed with overt diabetes and managed as such.
• Women with HbA1c 42–47 mmol/mol are at high risk of GDM. Glucose monitoring and dietary management is recommended from the second trimester.

Diagnosis test target levels Ireland:

HSE guidelines (recommendations for Ireland) for diagnosis are the following:

A diagnosis of gestational diabetes is made when one or more values are met or exceeded

• Fasting 5.1mmol/L
• 1 hour 10.0mmol/L
• 2 hour 8.5mmol/L

Borderline diagnosis

Borderline diagnosis can have very different meanings when it comes to gestational diabetes. It could mean that following your GTT your fasting or post-glucose levels were:

1. Just below the threshold targets
2. Bang on the threshold targets
3. Just over the threshold targets

Bearing in mind that test threshold target levels differ from one hospital to another, this could be a huge difference in actual blood glucose levels and therefore what is classed as borderline in one hospital may be clear positive test results in another.

The current NICE test targets have been questioned as to whether they are too low and missing around 4,000 cases of gestational diabetes per year.  This is shown by the University of Cambridge, New NICE thresholds could miss up to 4,000 women per year at risk from diabetes in pregnancy^​7​

With gestational diabetes being a progressive condition, it is very common for borderline-diagnosed women to have increased insulin resistance further into the pregnancy and many in fact, end up requiring medication to help control their levels, despite being ‘borderline’ on their initial test. For more information on borderline diagnosis and personal experiences after being told they have ‘borderline’ results, please read more here.

Why is diagnosing gestational diabetes important?

Having gestational diabetes means that a mother’s blood sugar levels remain too high. This means that excess glucose is passed through to the growing baby and can lead to complications for both the baby and the mother when giving birth.

PLEASE NOTE: Being diagnosed means that blood sugar levels can be monitored, and lowered and reduce related risks

Complications caused by gestational diabetes are:

• Macrosomia– your baby being large for its gestational age e. weighing more than 4kg (8.8lbs) Macrosomia increases the need for induced labour or caesarean birth and may lead to birth problems such as shoulder dystocia
• Shoulder dystocia – This is when your baby’s head passes through your vagina, but your baby’s shoulder gets stuck behind your pelvic bone. Shoulder dystocia can be dangerous, as your baby may not be able to breathe while they are stuck. It’s estimated to affect 1 in 200 births. Following shoulder dystocia deliveries, 20% of babies will suffer some sort of injury, either temporary or permanent. The most common of these injuries is damage to the brachial plexus nerves, fractured bones, contusions and lacerations, and birth asphyxia.
• Premature birth (your baby being born before week 37 of the pregnancy) – This can lead to complications such as newborn jaundice or respiratory distress syndrome (RDS).
• Polyhydramnios – Excessive amniotic fluid
• IUGR– Intrauterine growth restriction is a condition where a baby’s growth slows or ceases when it is in the uterus
• Pre-eclampsia
• Health problems shortly after birth that require hospital care – such as newborn hypoglycaemia (low blood sugar) and/or newborn jaundice
• Stillbirth – *It should be noted that whilst this is a complication of gestational diabetes, this is seen in cases where GD is not diagnosed or blood sugar levels are not monitored and/or controlled

What to do once diagnosed?

By reading the information on our website and joining our Facebook support group, we can help support you with how best to lower and stabilise blood sugar levels and ultimately help you manage the condition. From diagnosis to post-birth testing, we have all aspects of information covered to help you make informed choices and learn more based on what we’ve learnt through previous members and thorough evidence-based research.

Controversy surrounding the oral glucose tolerance test for diagnosing gestational diabetes

There is controversy surrounding the GTT due to two things:

1. The drink given to take the test
2. The amount of glucose given v’s the lack of exercise to help process the glucose during the test

1. The glucose drink used for diagnosis in the UK and ROI

Years ago, Lucozade was used for OGTTs, however when Lucozade reduced the amount of glucose in their drink a 75g glucose load would require in excess of 800ml of Lucozade! For this reason, most hospitals use a glucose replacement drink to conduct the OGTT.

You may see pictures of a glucose drink (Glucola) which is used in the USA for gestational diabetes testing and pictures of babies in the womb with slogans like “Mom, don’t drink the glucola” or “don’t drink this toxic drink“. The problem with Glucola is BVO, or brominated vegetable oil (a product that keeps the favouring from floating to the top of the drink) and it is found in many US drinks. Brominated vegetable oil is banned as a food additive in Europe under Regulation (EC) No 1333/2008.

Please note, this is NOT the same as the products used in the UK In the UK and Ireland, there are a few different glucose load options used:

Polycal:

• Ingredients (Neutral) Demineralised water, glucose syrup, maltodextrin, acidity regulator (citric acid).
• Ingredients (Orange) Demineralised water, glucose syrup, maltodextrin, acidity regulator (citric acid), flavour (orange), colour (curcumin, anthocyanins)

Rapilose: Ingredients Water, glucose syrup, glucose monohydrate, flavouring, citric acid (acidity regulator), potassium sorbate, sodium benzoate (preservatives)

Glucose monohydrate/ Glucose BP/ Dextrose monohydrate (dextrose powder)

If you have any concerns over the product used for diagnosing gestational diabetes, then you could ask to see the listed ingredients before taking the test.

For those who are reluctant to take a test based on the glucose drink, you could ask if your healthcare professionals would consider testing with a specific high-carbohydrate-load breakfast, although this is only allowed in exceptional circumstances and is no longer common practice.

2. Lack of activity following the high glucose load

With regards to not being allowed to be active between drinking the glucose and having further blood tests, I believe that if your pancreas is producing and using enough insulin i.e. non-diabetic, then your body will be able to process the glucose enough to show a negative result.

Is there another way to test without taking the GTT?

If you feel strongly that you do not want a GTT for diagnosing gestational diabetes, then you should discuss your reasons with your healthcare professionals.

Many hospitals will happily agree to home blood glucose monitoring which involves testing blood sugar levels at home with a blood glucose monitor and test strips.

Should I avoid or decline being tested?

Ultimately, it is up to each mother to make an informed choice of what is best for her baby and pregnancy. You cannot be forced to take any tests during pregnancy. Still, I highly advise looking at the complications gestational diabetes can have on your baby and you, many of which are symptomless.

A pregnancy diagnosed with gestational diabetes may mean more intervention, as you will be advised to test blood sugar levels regularly and will be referred for additional appointments at the hospital, alongside additional ultrasound scans. Then, depending on how well blood sugar levels can be managed, medication or insulin injections may be used. Having gestational diabetes may also mean that you could be advised to have your baby earlier than planned and in a hospital setting, under consultant-led care.

There are no certainties with gestational diabetes and some, or all of these interventions could be recommended. However it is up to each mother to decide which interventions to accept or decline. Use the B R A I N approach to help with making your decisions.

Monitoring blood sugar levels to record findings from fasting and after all meals would be a beneficial step, should you choose to refuse a GTT. Monitoring blood sugar levels is ultimately the most important thing in helping to manage the condition.

Refusing BOTH the GTT and monitoring blood sugar levels at home could lead to many complications for your baby should you have undiagnosed and uncontrolled blood sugar levels.

This study shows the importance of  screening for gestational diabetes in pregnancy.

A UK study published in BJOG (British Journal of Obstetrics and Gynaecology), 19 March 2019,  finds a 44% increase in stillbirth in women who are at risk of GD but not screened and a 4-fold greater risk of stillbirth in women with raised fasting levels who were not diagnosed. Yet they found the women who were screened and diagnosed with GD had no increase in stillbirth^​8​.

“Gestational diabetes just causes a bigger baby…”

Anyone who is under the assumption that gestational diabetes will ‘just cause a bigger baby… chubby babies are cute, bouncy babies!‘ and that this is the only concern should learn about the associated complications. There is a difference between a larger-sized baby and a baby who is swollen and very poorly due to undiagnosed or poorly controlled blood sugar levels.

Please read more here on the complications caused by gestational diabetes.

National guidelines for diabetes in pregnancy:-

NICE guidelines ng3 Diabetes in pregnancy: management of diabetes and its complications from preconception to the postnatal period

SIGN guidelines 116 Management of diabetes: A national clinical guideline

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

Research

1. 1.

   Marcinkevage JA, Narayan KMV. Gestational diabetes mellitus: Taking it to heart. Primary Care Diabetes. Published online July 2011:81-88. doi:10.1016/j.pcd.2010.10.002
2. 2.

   Wang C, Wei Y, Zhang X, et al. A randomized clinical trial of exercise during pregnancy to prevent gestational diabetes mellitus and improve pregnancy outcome in overweight and obese pregnant women. American Journal of Obstetrics and Gynecology. Published online April 2017:340-351. doi:10.1016/j.ajog.2017.01.037
3. 3.

   Martínez‐Vizcaíno V, Sanabria‐Martínez G, Fernández‐Rodríguez R, et al. Exercise during pregnancy for preventing gestational diabetes mellitus and hypertensive disorders: An umbrella review of randomised controlled trials and an updated meta‐analysis. BJOG. Published online October 17, 2022:264-275. doi:10.1111/1471-0528.17304
4. 4.

   What can help prevent gestational diabetes? Institute for Quality and Efficiency in Health Care (IQWiG). Published October 22, 2020. Accessed February 25, 2023. https://www.ncbi.nlm.nih.gov/books/NBK441575/
5. 5.

   Metz T. Coronavirus disease 2019 pandemic practice changes: more harm than good? BJOG: Int J Obstet Gy. Published online October 27, 2020:921-921. doi:10.1111/1471-0528.16550
6. 6.

   van‐de‐l’Isle Y, Steer P, Watt Coote I, Cauldwell M. Impact of changes to national UK Guidance on testing for gestational diabetes screening during a pandemic: a single‐centre observational study. BJOG: Int J Obstet Gy. Published online October 7, 2020:917-920. doi:10.1111/1471-0528.16482
7. 7.

   Meek CL, Lewis HB, Patient C, Murphy HR, Simmons D. Diagnosis of gestational diabetes mellitus: falling through the net. Diabetologia. Published online June 14, 2015:2003-2012. doi:10.1007/s00125-015-3647-z
8. 8.

   Stacey T, Tennant P, McCowan L, et al. Gestational diabetes and the risk of late stillbirth: a case–control study from England, UK. BJOG: Int J Obstet Gy. Published online March 19, 2019. doi:10.1111/1471-0528.15659