june 2019

What is gestational diabetes?

Gestational diabetes mellitus (GDM) is the development of diabetes in pregnancy, characterised by high blood glucose (sugar) levels during your pregnancy. GDM occurs during pregnancy when the hormone insulin is not being produced in the right amounts to match your body’s needs.

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what is gestational diabetes

It can be worrying finding out that you have suddenly developed diabetes during your pregnancy, but in most cases, it usually resolves once your baby has been born, as it is the pregnancy which puts extra strain upon your body’s insulin needs. In fact, GDM is not a rare condition but found in up to 16% of pregnancies.

How will I know if I have GDM?

To screen for GDM, you will be offered a glucose tolerance test (GTT) at 24-28 weeks of your pregnancy if you fall into a category where it is more likely that you could develop GDM. You will be offered a clinic appointment to attend where, after fasting, your blood will be tested. You will then have a glucose drink, wait a while and have another blood test to determine how well your body is dealing with regulating blood sugars. A fasting blood glucose greater than 5.6 and a post glucose drink test of 7.8 will mean the diagnosis of GDM.

Categories for GTT

  • BMI greater than 30 when you became pregnant.
  • Your family originates from the Middle East, The Caribbean, China or South Asia.
  • One of your parents or a sibling has diabetes.
  • You’ve had a baby before weighing greater than 10lbs or 4.5kgs.

Why is having GDM a problem?

You are more at risk of giving birth prematurely.

It is thought that having GDM during pregnancy can increase the incidence of developing pre-eclampsia, a condition which causes high blood pressure.

You are more likely to develop a condition called polyhydramnios, which is when there is an excess of amniotic fluid (your waters) around your baby. This can mean that you will be offered more check-ups during pregnancy.

The rate of stillbirth increases with GDM, but it is now thought this is also connected to unstable glucose levels and the GDM not being well managed during pregnancy. Therefore, careful management of GDM during pregnancy can help to stabilise glucose levels.

After the birth your baby may need extra monitoring due to their own blood sugars becoming unstable. This usually includes testing their blood glucose levels via a heel prick test.

Gestational diabetes is usually diagnosed during the 2nd trimester through the GTT, although if your midwife or doctor have concerns at any other time during your pregnancy they can offer you a GTT.

Managing a diagnosis of GDM

Most women can manage their GDM through diet and exercise. Your midwife or doctor will be able to advise you and recommend foods that are helpful to keep your blood sugars under control, as well as which foods to try to avoid.

If diet and exercise aren’t effective enough to control your glucose levels the next step is prescribed tablets called metformin.

In rare cases you may need to use injectable insulin to control your blood glucose levels. This may be because you cannot tolerate the oral medication, that the Metformin isn’t working to lower your blood glucose or that your blood glucose is very high.

You will be given a kit to monitor your blood sugar levels daily. It involves pricking your finger and putting a drop of blood onto a small machine which will then give you a glucose reading.

You will be offered extra scans to monitor your baby’s growth and development at 28, 32 and 36 weeks of your pregnancy.

What does GDM mean for labour and birth?

Induction of labour can vary in different hospitals for women with GDM and due to your own individual circumstances. National guidance from NICE (2015)* recommends induction should be offered by 40+6 if labour has not begun spontaneously.

If you decide that induction of labour is right for you and your baby, you will be admitted to hospital to start the induction process.

Once you are in labour, both you and your baby will be closely monitored. You will also have your blood glucose levels monitored hourly and you may have an insulin pump to help regulate your blood glucose levels.

Your baby’s blood glucose can become unstable after the birth, so will be monitored closely. To help to stabilise their blood glucose levels, try to feed your baby within the first hour of birth. If you are breastfeeding, ask your midwife about antenatal hand expressing from 36 weeks, as you can store expressed milk in case you need it for those first feeds.


Being diagnosed with gestational diabetes can be worrying for you at first, but it is more common than you think, so don’t panic, there are plenty of tips to help you manage and control this condition during your pregnancy.