Gestational diabetes often develops quietly. Most people feel no different, yet pregnancy hormones can make the body less responsive to insulin and allow blood glucose to rise. That is why gestational diabetes screening in the UK focuses on identifying people with a higher chance of developing the condition and offering a glucose tolerance test at the right stage of pregnancy.
Rising levels of overweight and obesity, alongside pregnancies at older ages, mean more families are hearing about gestational diabetes during antenatal care. The detail matters, though: a higher BMI is an established screening risk factor, while age alone is not used as a NICE risk factor in England. Scotland’s current NHS information does list being over 40 as a risk factor, so pathways can vary across the UK.
Who is offered gestational diabetes screening?
At your booking appointment, your midwife or doctor will review your medical and pregnancy history. Under NICE guidance, testing is offered if you have at least one recognised risk factor: a BMI of 30 kg/m² or above, gestational diabetes in a previous pregnancy, a previous baby weighing 4.5 kg or more, a parent or sibling with diabetes, or a family background associated with a higher prevalence of diabetes.
South Asian, Black Caribbean and Middle Eastern family origins are among those highlighted in NICE guidance. Some NHS services may also investigate if concerns arise later, such as repeated glucose in the urine, unexpectedly rapid fetal growth or excess amniotic fluid.
If you previously had gestational diabetes, testing may be arranged earlier. NICE recommends early self-monitoring of blood glucose or a 75 g oral glucose tolerance test soon after booking, followed by another test at 24 to 28 weeks if the early result is normal.
What happens during the glucose tolerance test in pregnancy?
The main GTT test used by NHS maternity services is the oral glucose tolerance test, usually shortened to OGTT. For people with standard risk factors, it is normally offered between 24 and 28 weeks because insulin resistance tends to increase as pregnancy progresses.
You will usually be asked to fast for around 8 to 10 hours. Plain water is often allowed, but follow the instructions from your own maternity unit. At the clinic, a blood sample is taken to measure fasting glucose. You then drink a measured glucose drink and rest. A second blood sample is taken two hours later to show how effectively your body has processed the glucose.
A practical tip is to book a morning appointment if you have a choice and take something suitable to eat afterwards. The test itself lasts about two hours, but check-in and waiting can make the visit longer. If you are unwell, vomiting or unable to fast as instructed, contact the maternity unit because illness may affect the test.
What do GTT results mean?
Under NICE diagnostic criteria, gestational diabetes is diagnosed if fasting plasma glucose is 5.6 mmol/L or higher, or if the two-hour level is 7.8 mmol/L or higher after the 75 g glucose drink. Only one result needs to reach the threshold. Your maternity team should interpret the result because local and national pathways can differ.
These diagnostic cut-offs are not the same as the glucose targets used after diagnosis. Once gestational diabetes is confirmed, the day-to-day targets for home monitoring are usually lower and are agreed with your clinical team.
Can you have gestational diabetes without symptoms?
Yes. Many people have no noticeable gestational diabetes symptoms. When symptoms occur, they can include increased thirst, urinating more often, tiredness, blurred vision, genital itching or recurrent thrush. Several are also common in ordinary pregnancy, so symptoms alone cannot confirm gestational diabetes.
If symptoms develop after a normal test, tell your midwife or doctor. Gestational diabetes can appear later, and your team can decide whether further assessment is needed.
What happens after a diagnosis?
Most people with gestational diabetes go on to have healthy pregnancies and healthy babies. Treatment aims to keep blood glucose within an agreed range and reduce the chance of problems such as a larger baby, birth difficulties, newborn low blood glucose and pre-eclampsia.
You will usually learn how to check glucose at home. Management often starts with food choices and appropriate activity. A diabetes diet in pregnancy is not a zero-carbohydrate diet and should not involve aggressive weight loss. The focus is generally regular balanced meals, sensible carbohydrate portions, higher-fibre choices, vegetables and protein, while limiting foods or drinks that cause sharp glucose rises.
For example, someone who gets a high reading after sweet cereal and juice may be advised to try a smaller portion of higher-fibre cereal with a protein-rich food, then compare readings. Changes should follow your maternity diabetes team’s advice rather than another person’s meal plan.
If these measures do not keep glucose in range, metformin or insulin may be recommended. Pregnancy hormones can make glucose difficult to control even when diet and activity are carefully managed.
Related internal topics worth exploring include prenatal screening tests, healthy eating in pregnancy, and what to expect at antenatal appointments.
What happens after the baby is born?
Gestational diabetes usually resolves after birth, but it increases the future risk of type 2 diabetes. Your NHS team should arrange follow-up blood testing after pregnancy, with timing depending on the pathway used in your part of the UK. Ongoing diabetes checks are then recommended, commonly every year. In a future pregnancy, tell your midwife about your history because earlier testing or monitoring may be offered.
Frequently asked questions
Is the glucose tolerance test compulsory in pregnancy?
No. It is offered to you, and you can discuss the benefits, limitations and concerns with your midwife or doctor. If you decline an OGTT, ask whether alternative monitoring is appropriate for your circumstances.
Can I drink water before a GTT?
Many NHS services allow plain water during the fasting period, but instructions can differ. Follow the leaflet or appointment information from your own maternity unit.
What if my GTT is normal but I later have symptoms?
Contact your midwife, GP or maternity team. A normal result earlier in pregnancy does not mean new symptoms should be ignored, particularly if there are also concerns about your baby’s growth or glucose in your urine.
How soon will I get my results?
Timing varies between NHS services. Some units contact patients quickly when results are abnormal, while others use their usual maternity results system. Ask your clinic when and how you should expect to hear.
Final thoughts
The glucose tolerance test is a straightforward but important part of risk-based prenatal care. Knowing why it is offered, how to prepare and what the numbers mean can make the process less confusing. If you are unsure whether you meet the screening criteria, or your circumstances change after an earlier normal test, speak to your maternity team so your screening plan reflects your individual risk and local NHS pathway.