The oral glucose tolerance test (OGTT) will be offered to some pregnant women between 24 and 28 weeks of pregnancy. If you have one or more risk factors for gestational diabetes, you should be offered this screening test. Risk factors may include your age, weight, medical history, family medical history, and ethnicity.

It is essential to have this test done because gestational diabetes comes with significant health risks for you and your baby and could complicate your labour and delivery. The OGTT may be done earlier if you have a high glucose level in your urine during your first midwife appointment, if you've had gestational diabetes in a previous pregnancy, or if you have a high risk for diabetes.

What does an OGTT involve, and what can I expect on the day?

At your booking appointment (the midwife appointment you have at 8-12 weeks of pregnancy), the midwife will ask you questions to identify your risk factors for gestational diabetes. Having one risk factor or more means you will be offered a screening at or before 28 weeks.

You will be asked to fast for eight to ten hours prior to the appointment, though you're usually allowed to have water. The test is performed by a doctor or midwife. You will have a blood test that morning and then be given a very sugary glucose drink (about 75 to 100 meals worth of sugar) and told to rest for two hours. Then another blood sample is taken to check how you've metabolised the glucose. You get the results back pretty quickly, usually within 24 hours, and, from there, your doctor will be able to diagnose gestational diabetes or your blood glucose level as normal.

What happens after I get my OGTT results?

If you are diagnosed with gestational diabetes, your healthcare team will stratify whether you need a little bit more TLC in pregnancy with more midwife appointments, blood sugar monitoring, and obstetrician appointments with ultrasounds. If your blood glucose level is normal, yours will likely remain a low-risk pregnancy where you simply see your midwife.

If you need an OGTT, the screening will be quite an important milestone in your pregnancy. It could change your experience quite a lot.

Is gestational diabetes common?

Gestational diabetes is fairly common, affecting one in twenty pregnancies in the UK every year, largely because of the strain pregnancy puts on mum's kidneys and metabolic system.

In severe cases, the symptoms will be similar to those of diabetes itself, and these include extreme thirst, frequent urination, blurred eyesight, and fatigue. In many cases, however, mum will have no symptoms at all, and this is another reason why the OGTT is important.

If I have gestational diabetes, why will I need extra support?

Diabetes is a medical complication that can alter pregnancy and delivery, as well as your health and your baby’s health after birth. It can impact not just your own blood sugars but also the growth of your baby and subsequently the blood sugars and the weight of the baby, as well as the baby's growth and development as a child. So, it's got quite far-reaching consequences.

If your healthcare team can monitor and manage your blood glucose level throughout the rest of the pregnancy, it will usually have a positive influence on the growth of your baby, the type of delivery you're having, and the health of your child after pregnancy.

So there's so many reasons to try and manage that blood glucose level effectively, be it through diet, tablets, or insulin injections, depending on how well you and your healthcare team think it's best to go about it.

If I have gestational diabetes, will I be diabetic for life?

Mum's diabetes will usually go away after birth, but, as this isn't the case for everyone, you will be tested to make sure you are in the clear. If it does go away after birth, it's important to remember that a history of gestational diabetes puts you at a significantly increased risk of Type 2 diabetes later on in life and remain mindful of your health.

For more evidence-based information on caring for yourself and your baby in pregnancy, take Unii's Pregnancy Journey video course with Dr. Shree Datta.

Why is the oral glucose tolerance test so important in pregnancy?

Unii looks at this screening for gestational diabetes.